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Insert and Update BULK XML data into SQL

2015-09-16T00:25:00.002-07:00

Problem

In my last article, I talked about how you can use an FTP task in SSIS to download files from an FTP server. But what if the file you have downloaded is an XML file and you need to import this data from the XML file into a SQL Server table? How do you process/parse XML data into SQL Server tables?

Solution

There are different ways to achieve this task of importing data from an XML file into a SQL Server table, but I am going to demonstrate one of easiest ways to accomplish this task.

These are the steps I performed for importing data into SQL Server and then parsing the XML into a relational format.

Import XML data from an XML file into SQL Server table using the OPENROWSET function
Parse the XML data using the OPENXML function

Importing XML data from XML file using OPENROWSET

I have an XML file downloaded from my FTP location to a local folder and data in this XML file looks like this:

Now in order to import data from the XML file to a table in SQL Server, I am using the OPENROWSET function as you can see below.

In the script below, I am first creating a table with a column of data type XML and then reading the XML data from the file using the OPENROWSET function by specifying the file location and name of the XML file as you can see below:

CREATE DATABASE OPENXMLTesting
GO


USE OPENXMLTesting
GO


CREATE TABLE XMLwithOpenXML
(
Id INT IDENTITY PRIMARY KEY,
XMLData XML,
LoadedDateTime DATETIME
)


INSERT INTO XMLwithOpenXML(XMLData, LoadedDateTime)
SELECT CONVERT(XML, BulkColumn) AS BulkColumn, GETDATE() 
FROM OPENROWSET(BULK 'D:\OpenXMLTesting.xml', SINGLE_BLOB) AS x;


SELECT * FROM XMLwithOpenXML

When I query the table in which I have imported the XML data, it looks like this. The XMLData column is an XML data type, it will output a hyperlink as shown below:

Clicking on the hyperlink, in the above image, will open another tab within SSMS with the XML data displayed as shown below.

<ROOT>
<Customers>
<Customer CustomerID="C001" CustomerName="Arshad Ali">
<Orders>
<Order OrderID="10248" OrderDate="2012-07-04T00:00:00">
<OrderDetail ProductID="10" Quantity="5" />
<OrderDetail ProductID="11" Quantity="12" />
<OrderDetail ProductID="42" Quantity="10" />
</Order>
</Orders>
<Address> Address line 1, 2, 3</Address>
</Customer>
<Customer CustomerID="C002" CustomerName="Paul Henriot">
<Orders>
<Order OrderID="10245" OrderDate="2011-07-04T00:00:00">
<OrderDetail ProductID="11" Quantity="12" />
<OrderDetail ProductID="42" Quantity="10" />
</Order>
</Orders>
<Address> Address line 5, 6, 7</Address>
</Customer>
<Customer CustomerID="C003" CustomerName="Carlos Gonzlez">
<Orders>
<Order OrderID="10283" OrderDate="2012-08-16T00:00:00">
<OrderDetail ProductID="72" Quantity="3" />
</Order>
</Orders>
<Address> Address line 1, 4, 5</Address>
</Customer>
</Customers>
</ROOT>

Process XML data using OPENXML function

Now as I said before, XML data stored in a column of data type XML can be processed either by using XML functions available in SQL Server or by using the sp_xml_preparedocument stored procedure along with the OPENXMLfunction.

We will first call the sp_xml_preparedocument stored procedure by specifying the XML data which will then output the handle of the XML data that it has prepared and stored in internal cache.

Then we will use the handle returned by the sp_xml_preparedocument stored procedure in the OPENXML function to open the XML data and read it.

Note: the sp_xml_preparedocument stored procedure stores the XML data in SQL Server's internal cache, it is essential to release this stored XML data from internal cache by calling the sp_xml_removedocument stored procedure. We should call the sp_xml_removedocument stored procedure as early possible, so that internal cache can be freed for other usage.

USE OPENXMLTesting
GO


DECLARE @XML AS XML, @hDoc AS INT, @SQL NVARCHAR (MAX)


SELECT @XML = XMLData FROM XMLwithOpenXML


EXEC sp_xml_preparedocument @hDoc OUTPUT, @XML


SELECT CustomerID, CustomerName, Address
FROM OPENXML(@hDoc, 'ROOT/Customers/Customer')
WITH 
(
CustomerID [varchar](50) '@CustomerID',
CustomerName [varchar](100) '@CustomerName',
Address [varchar](100) 'Address'
)


EXEC sp_xml_removedocument @hDoc
GO

From the above XML data, I want to retrieve all the customer information and hence I am navigating to the Customer element and querying CustomerID and CustomerName (please note the use of "@" before the name of the attribute) attributes and Address element in the above SELECT statement using the OPENXML function.

The structure of the resultset can be determined with the "WITH" clause as shown above.

From the above XML data, I now want to retrieve all the customer information along with OrderID and OrderDate placed by each individual customer and hence I am navigating to the Order element and then querying OrderID and OrderDate attributes.

If we want to navigate back to the parent or grand parent level and get data from there, we need to use "../" to read the parent's data and "../../" to read the grand parent's data and so on.

USE OPENXMLTesting
GO


DECLARE @XML AS XML, @hDoc AS INT, @SQL NVARCHAR (MAX)


SELECT @XML = XMLData FROM XMLwithOpenXML


EXEC sp_xml_preparedocument @hDoc OUTPUT, @XML


SELECT CustomerID, CustomerName, Address, OrderID, OrderDate
FROM OPENXML(@hDoc, 'ROOT/Customers/Customer/Orders/Order')
WITH 
(
CustomerID [varchar](50) '../../@CustomerID',
CustomerName [varchar](100) '../../@CustomerName',
Address [varchar](100) '../../Address',
OrderID [varchar](1000) '@OrderID',
OrderDate datetime '@OrderDate'
)


EXEC sp_xml_removedocument @hDoc
GO

The result of the above query can be seen in the image below. You can see below all the customers and all the orders placed by each customer.

Now let's go one level deeper. This time from the above XML data, I want to retrieve all the customer information and their orders along with ProductID and Quantity from each order placed. And hence, as you can see below I am navigating to the OrderDetail and retrieving the ProductID and Quantity attributes' values. At the same time I am using "../" to reach the parent level to get Order information available at the parent level whereas I am using "../../../" to reach to the great grand parent level to grab Customer information as shown below:

USE OPENXMLTesting
GO


DECLARE @XML AS XML, @hDoc AS INT, @SQL NVARCHAR (MAX)


SELECT @XML = XMLData FROM XMLwithOpenXML


EXEC sp_xml_preparedocument @hDoc OUTPUT, @XML


SELECT CustomerID, CustomerName, Address, OrderID, OrderDate, ProductID, Quantity
FROM OPENXML(@hDoc, 'ROOT/Customers/Customer/Orders/Order/OrderDetail')
WITH 
(
CustomerID [varchar](50) '../../../@CustomerID',
CustomerName [varchar](100) '../../../@CustomerName',
Address [varchar](100) '../../../Address',
OrderID [varchar](1000) '../@OrderID',
OrderDate datetime '../@OrderDate',
ProductID [varchar](50) '@ProductID',
Quantity int '@Quantity'
)


EXEC sp_xml_removedocument @hDoc
GO

The result of the above query can be seen in the image below. You can see all the customer information and their orders along with ProductID and Quantity from each order placed.

===============================================================

Update Query:

SELECT * FROM T
UPDATE T
SET XmlCol =(
SELECT * FROM OPENROWSET(
   BULK 'C:\SampleFolder\SampleData3.txt',
           SINGLE_BLOB
) AS x
)
WHERE IntCol = 1;
GO

Specification for SQL Server 2008,R2 and 2012

2015-09-15T02:42:00.003-07:00

SQL Server 2012 Maximum Capacity Specifications (32-bit Server)

The following tables specify the maximum sizes and numbers of various objects defined in SQL Server 2012 components, and compared against the maximum sizes and number of various objects defined in SQL Server 2008 and SQL Server 2008 R2 components.

Database Engine Objects

The following table specifies the maximum sizes and number of various objects defined in SQL Server databases or referenced in Transact-SQL statements.

Maximum Sizes / Numbers SQL Server (32-bit)
SQL Server Database Engine Object	SQL Server 2008	SQL Server 2008 R2	SQL Server 2012
Batch size	65,536 * Network Packet Size	65,536 * Network Packet Size	65,536 * Network Packet Size
Bytes per short string column	8,000	8,000	8,000
Bytes per GROUP BY ORDER BY	8,060	8,060	8,060
Bytes per index key	900	900	900
Bytes per foreign key	900	900	900
Bytes per primary key	900	900	900
Bytes per row	8,060	8,060	8,060
Bytes in source text of a stored procedure.	Lesser of batch size or 250 MB	Lesser of batch size or 250 MB	Lesser of batch size or 250 MB
Bytes per VARCHAR(MAX), VARBINARY(MAX),XML, TEXT, or IMAGE column	2^31-1	2^31-1	2^31-1
Characters per NTEXT or NVARCHAR(MAX) column	2^30-1	2^30-1	2^30-1
Clustered indexes per table	1	1	1
Columns in GROUP BY, ORDER BY	Limited only by number of bytes	Limited only by number of bytes	Limited only by number of bytes
Columns or expressions in a GROUP BY WITH CUBE or WITH ROLLUP statement	10	10	10
Columns per index key	16	16	16
Columns per foreign key	16	16	16
Columns per primary key	16	16	16
Columns per nonwide table	1,024	1,024	1,024
Columns per wide table	30,000	30,000	30,000
Columns per SELECT statement	4,096	4,096	4,096
Columns per INSERT statement	4,096	4,096	4,096
Connections per client	Maximum value of configured connections	Maximum value of configured connections	Maximum value of configured connections
Database size	524,272 terabytes	524,272 terabytes	524,272 terabytes
Databases per instance of SQL Server	32,767	32,767	32,767
Filegroups per database	32,767	32,767	32,767
Files per database	32,767	32,767	32,767
File size (data)	16 terabytes	16 terabytes	16 terabytes
File size (log)	2 terabytes	2 terabytes	2 terabytes
Foreign key table references per table	253	253	253
Identifier length (in characters)	128	128	128
Instances per computer	50 instances on a stand-alone server for all SQL Server editions.	50 instances on a stand-alone server for all SQL Server editions.	50 instances on a stand-alone server for all SQL Server editions.
Length of a string containing SQL statements (batch size)	65,536 * Network packet size	65,536 * Network packet size	65,536 * Network packet size
Locks per connection	Maximum locks per server	Maximum locks per server	Maximum locks per server
Locks per instance of SQL Server	Up to 2,147,483,647	Up to 2,147,483,647	Up to 2,147,483,647
Nested stored procedure levels	32	32	32
Nested subqueries	32	32	32
Nested trigger levels	32	32	32
Nonclustered indexes per table	999	999	999
Number of distinct expressions in the GROUP BY clause when any of the following are present: CUBE, ROLLUP, GROUPING SETS, WITH CUBE, WITH ROLLUP	32	32	32
Number of grouping sets generated by operators in the GROUP BY clause	4,096	4,096	4,096
Parameters per stored procedure	2,100	2,100	2,100
Parameters per user-defined function	2,100	2,100	2,100
REFERENCES per table	253	253	253
Rows per table	Limited by available storage	Limited by available storage	Limited by available storage
Tables per database	Limited by number of objects in a database	Limited by number of objects in a database	Limited by number of objects in a database
Partitions per partitioned table or index	1,000	1,000	15,000
Statistics on non-indexed columns	30,000	30,000	30,000
Tables per SELECT statement	Limited only by available resources	Limited only by available resources	Limited only by available resources
Triggers per table	Limited by number of objects in a database.	Limited by number of objects in a database.	Limited by number of objects in a database.
Columns per UPDATE statement (Wide Tables)	4,096	4,096	4,096
User connections	32,767	32,767	32,767
XML Indexes	249	249	249

SQL Server Utility Objects

The following table specifies the maximum sizes and number of various objects that were tested in the SQL Server Utility.

Maximum Sizes / Numbers SQL Server (32-bit)
SQL Server Utility Object	SQL Server 2008	SQL Server 2008 R2	SQL Server 2012
Computers (physical computers or virtual machines) per SQL Server Utility	100	100	100
Instances of SQL Server per computer	5	5	5
Total number of instances of SQL Server per SQL Server Utility	200	200	200
User databases per instance of SQL Server, including data-tier applications	50	50	50
Total number of user databases per SQL Server Utility	1,000	1,000	1,000
File groups per database	1	1	1
Data files per file group	1	1	1
Log files per database	1	1	1
Volumes per computer	3	3	3

SQL Server Data-Tier Application Objects

The following table specifies the maximum sizes and number of various objects that were tested in the SQL Server data-tier applications (DAC).

Maximum Sizes / Numbers SQL Server (32-bit)

SQL Server DAC Object

SQL Server 2008

SQL Server 2008 R2

SQL Server 2012

Databases per DAC

Objects per DAC

Limited by the number of objects in a database, or available memory.

SQL Server Replication Objects

The following table specifies the maximum sizes and number of various objects defined in SQL Server Replication.

Maximum Sizes / Numbers SQL Server (32-bit)
SQL Server Replication Object	SQL Server 2008	SQL Server 2008 R2	SQL Server 2012
Articles (merge publication)	256	256	256
Articles (snapshot or transactional publication)	32,767	32,767	32,767
Columns in a table (merge publication)	246	246	246
Columns in a table (SQL Server snapshot or transactional publication)	1,000	1,000	1,000
Columns in a table (Oracle snapshot or transactional publication)	995	995	995
Bytes for a column used in a row filter (merge publication)	1,024	1,024	1,024
Bytes for a column used in a row filter (snapshot or transactional publication)	8,000	8,000	8,000

ANROID Apps in .Net

2015-07-06T00:33:00.002-07:00

If you love C# and want to create an Android application using that language then you have to thank Xamarin as they created this great Cross Platform development tool which enables developers to develop iOS and Android apps in C# language. I tried developing before in Android but I did not like the experience in using the available IDE, as its slow and resource hungry, so I gave up. A couple of years after that I attended TechEd NZ 2013 and was introduced to this wonderful platform called Xamarin.

Xamarin is offered in different licenses from free to enterprise levels but for not I will be using the starter version which is the free version. It includes the Xamarin Studio which is great start for those who want to try out creating their first apps for Android, they also offer a Business license which lets you develop in Visual Studio so you can use that rich experience similar to developing Web Apps or Windows Apps, then they have this Enterprise which contains everything. For now lets see what the free stuff can offer, I did a simple project which I will be discussing below and it looks very promising, I love it.

Like what I said above we will be using the free version so we will make this simple project by using Xamarin Studio. Now I was thinking what to do, I don’t want to create the boring "Hello World!" demo so what I will be developing is a simple calculator which acts like a normal desk calculator. Most of the calculator projects online regardless its C#, VB.Net developed as Windows
forms does not act like a normal desk calculator where you can continuously perform operations and deliver results through the screen, you can’t even change operations along the way, so I decided I will make this one and I accepted my own challenge.

Lets start! First you need to download Xamarin at https://store.xamarin.com/, while installing it will ask you to download as well prerequisites but is you are a developer most or all of them are already set up in your machine.

Once its downloaded you’re ready to roll!

Fire up Xamarin Studio and select new Solution then Android Application, give it a solution name and in this case we use "Calculator".

Once all ok you will see the IDE which is like a cross between Visual Studio and Eclipse, it has intellisense and fancy text colours and highlighting.

You will notice if you go to the Resources\layout they the UI is in a file called Main.axml which is a "Hello World" template.

At this point we are more interested on the 2 files on the solution, that layout and the MainActivity.cs where we will be doing our coding.

First lets design you calculator, you need to go to that Main.axml and start coding, you will notice its like Windows form where you can drag and drop items from the Toolbox on the right, it will also have its property window on the bottom left.

Were not interested with the dragging and dropping part so let’s go the code behind (you can control it more), so hit that Source tab below the UI beside the content source. First thing you will notice is that it is in XML format, if you’re so used to drag and drop or HTML coding then you need a bit of learning here specially the layouts.

Common layouts used are Linear Layout, Relative Layout, List View and Grid View. To see how each of them would look like here is an illustration

Linear Layout – you can organize objects in either horizontal or vertical rows.

Relative Layout – specify the location of child objects relative to each other. For example object A is placed on the left of object B or it can be aligned to a parent.

List View – Displays it in a scrolling single column list.

Grid View – Displays it in a scrolling grid view of columns and rows.

Now lets start designing, for this project we will using a mix of Linear and Relative. Copy and Paste the code below then I will give you some explanation of what it does.

Hide Shrink Copy Code

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
  <EditText
      android:inputType="number"
      android:layout_width="fill_parent"
      android:layout_height="wrap_content"
      android:id="@+id/resultText" />
  <LinearLayout
android:id="@+id/wrapper0"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_below="@+id/resultText"
android:weightSum="1.0" >
    <Button
        android:text="Clear"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:id="@+id/buttonClear"
        android:layout_weight=".25" />
  </LinearLayout>
  <LinearLayout
android:id="@+id/wrapper1"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_below="@+id/wrapper0"
android:weightSum="1.0" >
    <Button
        android:text="1"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight=".25"
        android:id="@+id/button1" />
    <Button
        android:text="2"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@+id/button1"
        android:layout_alignTop="@+id/button1"
        android:layout_weight=".25"
        android:id="@+id/button2" />
    <Button
        android:text="3"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@+id/button2"
        android:layout_alignTop="@+id/button2"
        android:layout_weight=".25"
        android:id="@+id/button3" />
    <Button
        android:text="+"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@+id/button3"
        android:layout_alignTop="@+id/button3"
        android:layout_weight=".25"
        android:id="@+id/buttonAdd" />
  </LinearLayout>
  <LinearLayout
android:id="@+id/wrapper2"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_below="@+id/wrapper1"
android:weightSum="1.0" >
    <Button
        android:text="4"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@+id/wrapper2"
        android:layout_weight=".25"
        android:id="@+id/button4" />
    <Button
        android:text="5"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@+id/button4"
        android:layout_alignTop="@+id/button4"
        android:layout_weight=".25"
        android:id="@+id/button5" />
    <Button
        android:text="6"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@+id/button5"
        android:layout_alignTop="@+id/button5"
        android:layout_weight=".25"
        android:id="@+id/button6" />
    <Button
        android:text="-"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@+id/button6"
        android:layout_alignTop="@+id/button6"
        android:layout_weight=".25"
        android:id="@+id/buttonSubtract" />
  </LinearLayout>
  <LinearLayout
android:id="@+id/wrapper3"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_below="@+id/wrapper2"
android:weightSum="1.0" >
    <Button
        android:text="7"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@+id/wrapper3"
    android:layout_weight=".25"
        android:id="@+id/button7" />
    <Button
        android:text="8"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@+id/button7"
        android:layout_alignTop="@+id/button7"
        android:layout_weight=".25"
        android:id="@+id/button8" />
    <Button
        android:text="9"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@+id/button8"
        android:layout_alignTop="@+id/button8"
        android:layout_weight=".25"
        android:id="@+id/button9" />
    <Button
        android:text="x"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@+id/button9"
        android:layout_alignTop="@+id/button9"
        android:layout_weight=".25"
        android:id="@+id/buttonMultiply" />
  </LinearLayout>
  <LinearLayout
android:id="@+id/wrapper4"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_below="@+id/wrapper3"
android:weightSum="1.0" >
    <Button
        android:text="(-)"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@+id/button7"
        android:layout_weight=".25"
        android:id="@+id/buttonNegative" />
    <Button
        android:text="0"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@+id/buttonNegative"
        android:layout_alignTop="@+id/buttonNegative"
        android:layout_weight=".25"
        android:id="@+id/button0" />
    <Button
        android:text="."
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@+id/button0"
        android:layout_alignTop="@+id/buttonNegative"
        android:layout_weight=".25"
        android:id="@+id/buttonDot" />
    <Button
        android:text="/"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@+id/buttonDot"
        android:layout_alignTop="@+id/buttonDot"
        android:layout_weight=".25"
        android:id="@+id/buttonDivide" />
  </LinearLayout>
  <Button
      android:text="="
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:layout_below="@+id/wrapper4"
      android:id="@+id/buttonEquals" />
</RelativeLayout>

Most of the objects are created similar to an HTML tags like and <EditText>. Also like HTML Tags they will have properties and the common ones we used are:

orientation – this sets our object orientation either vertical or horizontal.
layout_width – fill_parent will fill depending on the parent with, you can also specify a with by using something like 200dp. If you want to use percentage use 0dp but we will be indicating percentage on layout_weight.
layout_height – similar to layout_width.
layout_weight – this indicated the percentage you will use on the width.
id – identifier to the object.
layout_toRightOf – this indicates you will place this object to the right of what object Id.
layout_alignTop – this aligns your object similar to what object Id.
layout_below – this will place your object below the object Id.

other elements would sound similar to .Net object properties. Now click your content tab to see how it looks. It should be something like this

Now you have your UI, you need to start coding in C#, so go to your MainActivity.cs

To display the layout you need to do this.

SetContentView (Resource.Layout.Main);

Then you will notice that objects are not natively available in code, you cant do something like this

resultText.Text = "";

you need to find it like how you find objects but ID in a grid during the ASP.Net days. To do it here is a sample for button1

Button button1 = FindViewById<Button> (Resource.Id.button1);

Now you have your button1, you can assign a delegate and define what it should do when you click

button1.Click += delegate {

//Your stuff here

};

Other than that you’re good to go, everything should be easy. So for the full code just copy and paste the one below, it’s an operational calculator.

Hide Shrink Copy Code

using System;
using Android.App;
using Android.Content;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.OS;

namespace SampleAndroidApp
{
    [Activity(Label = "Ray's Calculator", MainLauncher = true)]
    public class MainActivity : Activity
    {
        private enum Operation { Addition, Subtraction, Division, Multiplication };
        private enum LastKeyInput { Digit, Operator, Equal, DecimalPoint, Sign }

        decimal? digitMemory = null;
        decimal? totalMemory = null;

        Operation? operationMemory = null;

        LastKeyInput? lastKeyInput = LastKeyInput.Digit;

        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);

            // Set our view from the "main" layout resource
            SetContentView(Resource.Layout.Main);

            // Get our button from the layout resource,
            // and attach an event to it
            Button button1 = FindViewById(Resource.Id.button1);
            Button button2 = FindViewById(Resource.Id.button2);
            Button button3 = FindViewById(Resource.Id.button3);
            Button button4 = FindViewById(Resource.Id.button4);
            Button button5 = FindViewById(Resource.Id.button5);
            Button button6 = FindViewById(Resource.Id.button6);
            Button button7 = FindViewById(Resource.Id.button7);
            Button button8 = FindViewById(Resource.Id.button8);
            Button button9 = FindViewById(Resource.Id.button9);
            Button button0 = FindViewById(Resource.Id.button0);
            Button buttonDot = FindViewById(Resource.Id.buttonDot);
            Button buttonNegative = FindViewById(Resource.Id.buttonNegative);

            EditText resultText = FindViewById(Resource.Id.resultText);

            Button buttonAdd = FindViewById(Resource.Id.buttonAdd);
            Button buttonSubtract = FindViewById(Resource.Id.buttonSubtract);
            Button buttonMultiply = FindViewById(Resource.Id.buttonMultiply);
            Button buttonDivide = FindViewById(Resource.Id.buttonDivide);
            Button buttonEquals = FindViewById(Resource.Id.buttonEquals);
            Button buttonClear = FindViewById(Resource.Id.buttonClear);

            buttonNegative.Click += delegate
            {
                //handles if negative sign is the first input after calculation
                if (lastKeyInput != LastKeyInput.Digit && lastKeyInput != LastKeyInput.DecimalPoint && lastKeyInput != LastKeyInput.Sign)
                {
                    resultText.Text = "-";
                    lastKeyInput = LastKeyInput.Sign;
                    return;
                }
                //handles multiple negative sign
                if (!resultText.Text.Contains("-"))
                {
                    resultText.Text = "-" + digitMemory.ToString();
                    lastKeyInput = LastKeyInput.Sign;
                }

            };
            buttonDot.Click += delegate
            {
                //handles if decimal point is the first input after calculation
                if (lastKeyInput != LastKeyInput.Digit && lastKeyInput != LastKeyInput.DecimalPoint && lastKeyInput != LastKeyInput.Sign)
                {
                    resultText.Text = ".";
                    lastKeyInput = LastKeyInput.DecimalPoint;
                    return;
                }
                //handles multiple decimal point
                if (!resultText.Text.Contains("."))
                {
                    resultText.Text = digitMemory.ToString() + ".";
                    lastKeyInput = LastKeyInput.DecimalPoint;
                }

            };
            button1.Click += delegate
            {
                //Renders Text on Screen
                RenderCurrentValue(resultText.Text, "1");
                resultText.Text = digitMemory.ToString();

                //Perform calculation based on current operator
                Calculate();
                lastKeyInput = LastKeyInput.Digit;
            };

            button2.Click += delegate
            {
                RenderCurrentValue(resultText.Text, "2");
                resultText.Text = digitMemory.ToString();
                Calculate();
                lastKeyInput = LastKeyInput.Digit;
            };

            button3.Click += delegate
            {
                RenderCurrentValue(resultText.Text, "3");
                resultText.Text = digitMemory.ToString();
                Calculate();
                lastKeyInput = LastKeyInput.Digit;
            };

            button4.Click += delegate
            {
                RenderCurrentValue(resultText.Text, "4");
                resultText.Text = digitMemory.ToString();
                Calculate();
                lastKeyInput = LastKeyInput.Digit;
            };

            button5.Click += delegate
            {
                RenderCurrentValue(resultText.Text, "5");
                resultText.Text = digitMemory.ToString();
                Calculate();
                lastKeyInput = LastKeyInput.Digit;
            };

            button6.Click += delegate
            {
                RenderCurrentValue(resultText.Text, "6");
                resultText.Text = digitMemory.ToString();
                Calculate();
                lastKeyInput = LastKeyInput.Digit;
            };

            button7.Click += delegate
            {
                RenderCurrentValue(resultText.Text, "7");
                resultText.Text = digitMemory.ToString();
                Calculate();
                lastKeyInput = LastKeyInput.Digit;
            };

            button8.Click += delegate
            {
                RenderCurrentValue(resultText.Text, "8");
                resultText.Text = digitMemory.ToString();
                Calculate();
                lastKeyInput = LastKeyInput.Digit;
            };

            button9.Click += delegate
            {
                RenderCurrentValue(resultText.Text, "9");
                resultText.Text = digitMemory.ToString();
                Calculate();
                lastKeyInput = LastKeyInput.Digit;
            };

            button0.Click += delegate
            {
                RenderCurrentValue(resultText.Text, "0");
                resultText.Text = digitMemory.ToString();
                Calculate();
                lastKeyInput = LastKeyInput.Digit;
            };

            buttonClear.Click += delegate
            {
                resultText.Text = "";
                ResetMemory();
            };

            buttonAdd.Click += delegate
            {
                if (lastKeyInput == LastKeyInput.Digit || lastKeyInput == LastKeyInput.Operator)
                {
                    operationMemory = Operation.Addition;
                }
                resultText.Text = totalMemory.ToString();
                lastKeyInput = LastKeyInput.Operator;
            };

            buttonSubtract.Click += delegate
            {
                if (lastKeyInput == LastKeyInput.Digit || lastKeyInput == LastKeyInput.Operator)
                {
                    operationMemory = Operation.Subtraction;
                }
                resultText.Text = totalMemory.ToString();
                lastKeyInput = LastKeyInput.Operator;
            };

            buttonMultiply.Click += delegate
            {
                if (lastKeyInput == LastKeyInput.Digit || lastKeyInput == LastKeyInput.Operator)
                {
                    operationMemory = Operation.Multiplication;
                }
                resultText.Text = totalMemory.ToString();
                lastKeyInput = LastKeyInput.Operator;
            };

            buttonDivide.Click += delegate
            {
                if (lastKeyInput == LastKeyInput.Digit || lastKeyInput == LastKeyInput.Operator)
                {
                    operationMemory = Operation.Division;
                }
                resultText.Text = totalMemory.ToString();
                lastKeyInput = LastKeyInput.Operator;
            };

            buttonEquals.Click += delegate
            {
                lastKeyInput = LastKeyInput.Equal;
                resultText.Text = totalMemory.ToString();
                ResetMemory();
            };

        }

        private void Calculate()
        {
            if (operationMemory != null)
            {
                switch (operationMemory)
                {
                    case Operation.Addition:
                        if (totalMemory == null)
                        {
                            //Handles first entry
                            totalMemory = digitMemory;
                        }
                        else
                        {
                            totalMemory = totalMemory + digitMemory;
                        }
                        lastKeyInput = LastKeyInput.Operator;
                        break;

                    case Operation.Subtraction:
                        if (totalMemory == null)
                        {
                            //Handles first entry
                            totalMemory = digitMemory;
                        }
                        else
                        {
                            totalMemory = totalMemory - digitMemory;
                        }
                        lastKeyInput = LastKeyInput.Operator;
                        break;

                    case Operation.Multiplication:
                        if (totalMemory == null)
                        {
                            //Handles first entry
                            totalMemory = digitMemory;
                        }
                        else
                        {
                            totalMemory = totalMemory * digitMemory;
                        }
                        lastKeyInput = LastKeyInput.Operator;
                        break;

                    case Operation.Division:
                        if (totalMemory == null)
                        {
                            //Handles first entry
                            totalMemory = digitMemory;
                        }
                        else
                        {
                            totalMemory = totalMemory / digitMemory;
                        }
                        lastKeyInput = LastKeyInput.Operator;
                        break;
                }
            }
            else
            {

                totalMemory = digitMemory;

            }
        }

        private void RenderCurrentValue(string currentRenderedValue, string character)
        {
            //display multiple digits
            if (lastKeyInput == LastKeyInput.Digit || lastKeyInput == LastKeyInput.DecimalPoint || lastKeyInput == LastKeyInput.Sign)
            {
                digitMemory = decimal.Parse(currentRenderedValue + character);
            }
            else
            {
                digitMemory = decimal.Parse(character);
            }
        }

        private void ResetMemory()
        {
            totalMemory = null;
            digitMemory = null;
            operationMemory = null;
            lastKeyInput = LastKeyInput.Digit;
        }
    }

}

Just a side note : You might notice Calculate happens on each digit press, this makes sure you have a running total even before you hit the operator. The operator buttons will just store the current operator needed for your next digit press.

Other than that you are now all good to go, just hit run

It will now ask you for a device, if you don’t have an emulator yet then you can create one, choose create emulator then hit OK.

Click New

Then I suggest create something similar to a device you have, so you can play around with it on your device.

Once created hit start, then launch

You will now see it will start, and it will also show you any errors it encounter.

Once started go back to Xamarin and choose the device you want your app to run on, in this case your newly created emulator, it will then be automatically deployed on the emulator.

You will then see the progress on the middle top part of the IDE.

Then on your emulator

LINQ Joins

2015-07-06T00:28:00.004-07:00

There are Different Types of SQL Joins which are used to query data from more than one tables. In this article, I would like to share how joins work in LINQ. LINQ has a JOIN query operator that provide SQL JOIN like behavior and syntax. Let's see how JOIN query operator works for joins. This article will explore the SQL Joins with C# LINQ.

INNER JOIN
LEFT OUTER JOIN
CROSS JOIN
GROUP JOIN

The JOIN query operator compares the specified properties/keys of two collections for equality by using the EQUALS keyword. By default, all joins queries written by the JOIN keyword are treated as equijoins.

LINQ PAD for running and debugging LINQ Query

I am a big fan of LINQ Pad since it allow us to run LINQ to SQL and LINQ to Entity Framework query and gives the query output. Whenever, I need to write LINQ to SQL and LINQ to Entity Framework query then, I prefer to write and run query on LINQ PAD. By using LINQ PAD, you can test and run your desired LINQ query and avoid the head-ache for testing LINQ query with in Visual Studio. You can download the LINQ Pad script used in this article by using this link.

In this article, I am using LINQ PAD for query data from database. It is simple and useful. For more help about LINQ PAD refer the link. You can download the database script used in this article by using this link. Suppose we following three tables and data in these three tables is shown in figure.

INNER JOIN

Inner join returns only those records or rows that match or exists in both the tables.

C# Code


 var q=(from pd in dataContext.tblProducts join od in dataContext.tblOrders on pd.ProductID equals od.ProductID orderby od.OrderID select new { od.OrderID,
 pd.ProductID,
 pd.Name,
 pd.UnitPrice,
 od.Quantity,
 od.Price,
 }).ToList();

LINQ Pad Query

INNER JOIN among more than two tables

Like SQL, we can also apply join on multiple tables based on conditions as shown below.

C# Code


 var q=(from pd in dataContext.tblProducts join od in dataContext.tblOrders on pd.ProductID equals od.ProductID join ct in dataContext.tblCustomers on od.CustomerID equals ct.CustID orderby od.OrderID select new { od.OrderID,
 pd.ProductID,
 pd.Name,
 pd.UnitPrice,
 od.Quantity,
 od.Price,
 Customer=ct.Name //define anonymous type Customer
 }).ToList();

LINQ Pad Query

INNER JOIN On Multiple Conditions

Sometimes, we required to apply join on multiple coditions. In this case, we need to make two anonymous types (one for left table and one for right table) by using new keyword then we compare both the anonymous types.

C# Code


 var q=(from pd in dataContext.tblProducts join od in dataContext.tblOrders on pd.ProductID equals od.ProductID join ct in dataContext.tblCustomers on new {a=od.CustomerID,b=od.ContactNo} equals new {a=ct.CustID,b=ct.ContactNo} orderby od.OrderID select new { od.OrderID,
 pd.ProductID,
 pd.Name,
 pd.UnitPrice,
 od.Quantity,
 od.Price,
 Customer=ct.Name //define anonymous type Customer
 }).ToList();

LINQ Pad Query

NOTE

Always remember, both the anonymous types should have exact same number of properties with same name and datatype other wise you will get the compile time error "Type inferencce failed in the call to Join".
Both the comparing fields should define either NULL or NOT NULL values.
If one of them is defined NULL and other is defined NOT NULL then we need to do typecasting of NOT NULL field to NULL data type like as above fig.

LEFT JOIN or LEFT OUTER JOIN

LEFT JOIN returns all records or rows from left table and from right table returns only matched records. If there are no columns matching in the right table, it returns NULL values.

In LINQ to achieve LEFT JOIN behavior, it is mandatory to use "INTO" keyword and "DefaultIfEmpty()" method. We can apply LEFT JOIN in LINQ like as :

C# Code


 var q=(from pd in dataContext.tblProducts join od in dataContext.tblOrders on pd.ProductID equals od.ProductID into t from rt in t.DefaultIfEmpty() orderby pd.ProductID select new { //To handle null values do type casting as int?(NULL int) 
 //since OrderID is defined NOT NULL in tblOrders
 OrderID=(int?)rt.OrderID,
 pd.ProductID,
 pd.Name,
 pd.UnitPrice,
 //no need to check for null since it is defined NULL in database
 rt.Quantity,
 rt.Price,
 }).ToList();

LINQ Pad Query

CROSS JOIN

Cross join is a cartesian join means cartesian product of both the tables. This join does not need any condition to join two tables. This join returns records or rows that are multiplication of record number from both the tables means each row on left table will related to each row of right table.

In LINQ to achieve CROSS JOIN behavior, there is no need to use Join clause and where clause. We will write the query as shown below.

C# Code


 var q = from c in dataContext.Customers from o in dataContext.Orders select new { c.CustomerID,
 c.ContactName,
 a.OrderID,
 a.OrderDate
 };

LINQ Pad Query

GROUP JOIN

Whene a join clause use an INTO expression, then it is called a group join. A group join produces a sequence of object arrays based on properties equivalence of left collection and right collection. If right collection has no matching elements with left collection then an empty array will be produced.

C# Code


 var q=(from pd in dataContext.tblProducts join od in dataContext.tblOrders on pd.ProductID equals od.ProductID into t orderby pd.ProductID
 select new
 {
 pd.ProductID,
 pd.Name,
 pd.UnitPrice,
 Order=t
 }).ToList();

LINQ Pad Query

Basically, GROUP JOIN is like as INNER-EQUIJOIN except that the result sequence is organized into groups.

GROUP JOIN As SubQuery

We can also use the result of a GROUP JOIN as a subquery like as:

C# Code


 var q=(from pd in dataContext.tblProducts join od in dataContext.tblOrders on pd.ProductID equals od.ProductID into t from rt in t where rt.Price>70000 orderby pd.ProductID select new { rt.OrderID,
 pd.ProductID,
 pd.Name,
 pd.UnitPrice,
 rt.Quantity,
 rt.Price,
 }).ToList();

LINQ Pad Query

Active Directory in C#.Net

2014-08-12T02:44:00.000-07:00

Microsoft Technet offers a script repository to work with AD User Accounts; however, I needed to work with .NET and I could not find samples for all the tasks I needed to program. I promised to myself that one day I would publish the code samples I found and created to help other developers who are working with Directory Services. So, I wish you a happy AD.NET programming and I hope my work saves you some time. The code samples I provide are written in C#.
1. Create a connection to Active Directory
/// <summary>/// Method used to create an entry to the AD./// Replace the path, username, and password./// </summary>/// <returns>DirectoryEntry</returns>public static DirectoryEntry GetDirectoryEntry()
{
DirectoryEntry de = new DirectoryEntry();
de.Path = LDAP://192.168.1.1/CN=Users;DC=Yourdomain;
de.Username = @"yourdomain\sampleuser";
de.Password = "samplepassword";return de;
}
2. Create a secure connection to Active Directory
To connect to the AD, you need a user account that belongs to the domain you want to connect to. Most user accounts have permissions to search the AD; however, to modify the AD, you need a user account that is a member of the group of Domain Administrators (DomainAdmin). An account that belongs to this group has high privileges and hardcoding the user and password of this account in your code can compromise the security of the AD. I don't recommend you to create directory entries where usernames and passwords are hardcoded. Try to connect to the AD using a secure connection.
/// <summary>/// Method used to create an entry to the AD using a secure connection./// Replace the path./// </summary>/// <returns>DirectoryEntry</returns>public static DirectoryEntry GetDirectoryEntry()
{
DirectoryEntry de = new DirectoryEntry();
de.Path = LDAP://192.168.1.1/CN=Users;DC=Yourdomain;
de.AuthenticationType = AuthenticationTypes.Secure;return de;
}
To connect to the AD using a secure connection, you need to delegate the permissions of a user account with DomainAdmin permissions to the thread that is running a program. For instance, I created an exe and I ran the program using the Run As command to start a program. I delegated the user's principal identity and culture to the current thread that runs the program. To delegate the principal identity and culture to the current thread, I used the following code:
/// <summary>/// Establish identity (principal) and culture for a thread./// </summary>public static void SetCultureAndIdentity()
{
AppDomain.CurrentDomain.SetPrincipalPolicy(PrincipalPolicy.WindowsPrincipal);
WindowsPrincipal principal = (WindowsPrincipal)Thread.CurrentPrincipal;
WindowsIdentity identity = (WindowsIdentity)principal.Identity;
System.Threading.Thread.CurrentThread.CurrentCulture = new CultureInfo("en-US");
}
3. Validate if a user exists
/// <summary>/// Method to validate if a user exists in the AD./// </summary>/// <param name="UserName"></param>/// <returns></returns>public bool UserExists(string UserName)
{
DirectoryEntry de = ADHelper.GetDirectoryEntry();
DirectorySearcher deSearch = new DirectorySearcher();
deSearch.SearchRoot =de;
deSearch.Filter = "(&(objectClass=user) (cn=" + UserName +"))";
SearchResultCollection results = deSearch.FindAll();if(results.Count == 0)
{return false;
}else{return true;
}
}
4. Set user's properties
/// <summary>/// Helper method that sets properties for AD users./// </summary>/// <param name="de"></param>/// <param name="PropertyName"></param>/// <param name="PropertyValue"></param>public static void SetProperty(DirectoryEntry de, string PropertyName, string PropertyValue)
{if(PropertyValue!=null)
{if(de.Properties.Contains(PropertyName))
{
de.Properties[PropertyName][0]=PropertyValue;
}else{
de.Properties[PropertyName].Add(PropertyValue);
}
}
5. Set user's country
To set the country property for a user was one of the tasks that took me some time to figure out. After some hours of research I realized that you need to know the ISO 3166 Codes for countries and set three properties to define a user's country: c, co, and countryCode.
// Set the co property using the name of the country.SetProperty(newuser,"co","MEXICO");// Set the c property using the two-letter country code (ISO 3166 A 2).SetProperty(newuser,"c","MX");// Set the countryCode property using the numeric value (ISO 3166 Number) of the country.SetProperty(newuser,"countryCode","484");}
6. Set user's password
Setting the password for a user requires some work. I will walk you through the steps I followed to set a password for a user:
a) Create or download a helper class that generates random passwords that comply with the strong password rules. I was short of time and couldn't develop one, so I downloaded the RandomPassword class created by Obviex.b) Create a method that consumes the RandomPassword helper class
/// <summary>/// Method that consumes a helper class library/// to generate random passwords./// </summary>/// <returns></returns>public string SetSecurePassword()
{
RandomPassword rp = new RandomPassword();return rp.Generate(8,8);
}
c) Set the password property using the usr.Invoke method.
/// <summary>/// Method to set a user's password/// <param name="path"></param>public void SetPassword(string path)
{
DirectoryEntry usr = new DirectoryEntry();
usr.Path = path;
usr.AuthenticationType = AuthenticationTypes.Secure;object[] password = new object[] {SetSecurePassword()};object ret = usr.Invoke("SetPassword", password );
usr.CommitChanges();
usr.Close();}
The usr.Invoke method can be called once within the same AppDomain, otherwise your program will crash. If you place a call to the usr.Invoke method inside a for construct, the first run will be succesful, but the second one will crash the compiler. I created a workaround that helped me to solve this problem. I made a separate console application (SetPassword.exe) and I called and started the process programatically from the SetPassword method.

Download the SetPassword project.
Copy the SetPassword.exe file in your application.
Call and start SetPassword.exe from your application.

/// </summary>/// Method that calls and starts SetPassword.exe/// <param name="path"></param>/// <param name="password"></param>public void SetPassword(string path, string password)
{
StringBuilder args = new StringBuilder();
args.Append(path);
args.Append(" ");
args.Append(password);
ProcessStartInfo startInfo = new ProcessStartInfo("SetPassword.exe",args.ToString());
startInfo.WindowStyle = ProcessWindowStyle.Hidden;
Process.Start(startInfo);
}
7. Enable a user account
/// <summary>/// Method to enable a user account in the AD./// </summary>/// <param name="de"></param>private static void EnableAccount(DirectoryEntry de)
{//UF_DONT_EXPIRE_PASSWD 0x10000int exp = (int) de.Properties["userAccountControl"].Value;
de.Properties["userAccountControl"].Value = exp | 0x0001;de.CommitChanges();//UF_ACCOUNTDISABLE 0x0002int val = (int) de.Properties["userAccountControl"].Value;
de.Properties["userAccountControl"].Value = val & ~0x0002;
de.CommitChanges();
}
8. Add a user to a group
/// <summary>/// Method to add a user to a group/// </summary>/// <param name="de"></param>/// <param name="deUser"></param>/// <param name="GroupName"></param>public static void AddUserToGroup(DirectoryEntry de, DirectoryEntry deUser, string GroupName)
{
DirectorySearcher deSearch = new DirectorySearcher();
deSearch.SearchRoot = de;
deSearch.Filter = "(&(objectClass=group) (cn=" + GroupName +"))";
SearchResultCollection results = deSearch.FindAll();bool isGroupMember = false;if (results.Count>0)
{
DirectoryEntry group = GetDirectoryEntry(results[0].Path);object members = group.Invoke("Members",null);foreach ( object member in (IEnumerable) members)
{
DirectoryEntry x = new DirectoryEntry(member);if (x.Name! = deUser.Name)
{
isGroupMember = false;
}else{
isGroupMember = true;break;
}
}if (!isGroupMember)
{
group.Invoke("Add", new object[] {deUser.Path.ToString()});
}
group.Close();
}return;
}
9. Generate a mailbox for a user in Microsoft Exchange Server
You might need to create a mailbox for a user in Microsoft Exchange Server. Network configuration and server architecture can add complexity to the process of programmatically creating mailboxes for users, but you know, there's always a workaround. You can invoke a script that creates mailboxes from a remote machine. I will walk you through the steps I followed to create a mailbox for a user in Microsoft Exchange Server.

On the Domain Controller server, create the directory C:\TestRemoteMailbox.
Download the scripts MailBox.vbs and WSHControl.vbs.
Copy the script Mailbox.vbs to the directory C:\TestRemoteMailbox.
Note: Mailbox.vbs is a script that creates MailBoxes in Microsoft Exchange.
Copy the script WSHControl.vbs to your application directory.
Note: WSHControl.vbs is a script that invokes the MailBox.vbs script on a remote machine (Domain Controller)
From your application, call and start WSHControl.vbs.

/// <summary>/// Method that calls and starts a WSHControl.vbs/// </summary>/// <param name="userAlias"></param>public void GenerateMailBox(string userAlias)
{
StringBuilder mailargs = new StringBuilder();
mailargs.Append("WSHControl.vbs");
mailargs.Append(" ");
mailargs.Append(userAlias);
ProcessStartInfo sInfo = new ProcessStartInfo("Wscript.exe",mailargs.ToString());
sInfo.WindowStyle = ProcessWindowStyle.Hidden;;
Process.Start(sInfo);
}
10. Create a user account
/// <summary>/// Method that creates a new user account/// </summary>/// <param name="employeeID"></param>/// <param name="name"></param>/// <param name="login"></param>/// <param name="email"></param>/// <param name="group"></param>public void CreateNewUser(string employeeID, string name, string login, string email, string group)
{
Catalog catalog = new Catalog();
DirectoryEntry de = ADHelper.GetDirectoryEntry();/// 1. Create user accountDirectoryEntries users = de.Children;
DirectoryEntry newuser = users.Add("CN=" + login, "user");/// 2. Set propertiesSetProperty(newuser,"employeeID", employeeID);
SetProperty(newuser,"givenname", name);
SetProperty(newuser,"SAMAccountName", login);
SetProperty(newuser,"userPrincipalName", login);
SetProperty(newuser,"mail", email);
newuser.CommitChanges();/// 3. Set passwordSetPassword(newuser.Path);
newuser.CommitChanges();/// 4. Enable account EnableAccount(newuser);/// 5. Add user account to groupsAddUserToGroup(de,newuser,group);/// 6. Create a mailbox in Microsoft Exchange GenerateMailBox(login);
newuser.Close();
de.Close();
}
11. Disable a user account
/// <summary>/// Method that disables a user account in the AD and hides user's email from Exchange address lists./// </summary>/// <param name="EmployeeID"></param>public void DisableAccount(string EmployeeID)
{
DirectoryEntry de = GetDirectoryEntry();
DirectorySearcher ds = new DirectorySearcher(de);
ds.Filter = "(&(objectCategory=Person)(objectClass=user)(employeeID=" + EmployeeID + "))";
ds.SearchScope = SearchScope.Subtree;
SearchResult results = ds.FindOne();if(results != null)
{
DirectoryEntry dey = GetDirectoryEntry(results.Path);int val = (int)dey.Properties["userAccountControl"].Value;
dey.Properties["userAccountControl"].Value = val | 0x0002;
dey.Properties["msExchHideFromAddressLists"].Value = "TRUE";
dey.CommitChanges();
dey.Close();
}
de.Close();
}
12. Update user account
/// <summary>/// Method that updates user's properties/// </summary>/// <param name="employeeID"></param>/// <param name="department"></param>/// <param name="title"></param>/// <param name="company"></param>public void ModifyUser(string employeeID, string department, string title, string company)
{
DirectoryEntry de = GetDirectoryEntry();
DirectorySearcher ds = new DirectorySearcher(de);
ds.Filter = "(&(objectCategory=Person)(objectClass=user)(employeeID=" + employeeID + "))";
ds.SearchScope = SearchScope.Subtree;
SearchResult results = ds.FindOne();if(results!=null)
{
DirectoryEntry dey = GetDirectoryEntry(results.Path);
SetProperty(dey, "department", department);
SetProperty(dey, "title", title);
SetProperty(dey, "company", company);
dey.CommitChanges();
dey.Close();
}
de.Close();
}
13. Validate if a string has a correct email pattern.
/// <summary>/// Method that validates if a string has an email pattern./// </summary>/// <param name="mail"></param>/// <returns></returns>public bool IsEmail(string mail)
{
Regex mailPattern = new Regex(@"\w+([-+.]\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*");return mailPattern.IsMatch(mail);
}
14. Extract a user alias from an email account.
/// <summary>/// Method to extract the alias from an email account./// dada una cuenta de correo electrÃ³nico/// </summary>/// <param name="mailAddress"></param>/// <returns></returns>public string GetAlias(string mailAddress)
{if (IsEmail(mailAddress))
{return mailAddress.Substring(0,mailAddress.IndexOf("@"));
}else{return "";
}
}
15. Format dates to AD date format (AAAAMMDDMMSSSS.0Z)
/// <summary>/// Method that formats a date in the required format/// needed (AAAAMMDDMMSSSS.0Z) to compare dates in AD./// </summary>/// <param name="date"></param>/// <returns>Date in valid format for AD</returns>public string ToADDateString(DateTime date)
{string year = date.Year.ToString();int month = date.Month;int day = date.Day;
StringBuilder sb = new StringBuilder();
sb.Append(year);if (month <10)
{
sb.Append("0");
}
sb.Append(month.ToString());if (day <10)
{
sb.Append("0");
}
sb.Append(day.ToString());
sb.Append("000000.0Z");return sb.ToString();
}
16. Search users
When you use Directory Services, you can accomplish many interesting tasks such as searching and filtering users. The DirectorySearcher object allows you to query the AD. The following sample code queries the AD to search all the user accounts that were modified from a given date. The results are stored in a DataTable, so you can easily databind them.
/// <summary>/// Method that returns a DataTable with a list of users modified from a given date./// </summary>/// <param name="fromdate"></param>public DataTable GetModifiedUsers(DateTime fromdate)
{
DataTable dt = new DataTable();
dt.Columns.Add("EmployeeID");
dt.Columns.Add("Name");
dt.Columns.Add("Email");
DirectoryEntry de = GetDirectoryEntry();
DirectorySearcher ds = new DirectorySearcher(de);
StringBuilder filter = new StringBuilder();
filter.Append("(&(objectCategory=Person)(objectClass=user)(whenChanged>=");
filter.Append(date.ToADDateString());
filter.Append("))");
ds.Filter=filter.ToString();
ds.SearchScope = SearchScope.Subtree;
SearchResultCollection results= ds.FindAll();foreach(SearchResult result in results)
{
DataRow dr = dt.NewRow();
DirectoryEntry dey = GetDirectoryEntry(result.Path);
dr["EmployeeID"] = dey.Properties["employeeID"].Value;
dr["Name"] = dey.Properties["givenname"].Value;
dr["Email"] = dey.Properties["mail"].Value;
dt.Rows.Add(dr);
dey.Close();
}
de.Close();return dt;
}

jQuery 1.4 New Features you Must Know

2014-07-23T22:43:00.001-07:00

jQuery 1.4 was recently released. This wasn't simply a maintenance release as some had speculated; there are many new features, enhancements and performance improvements included in 1.4! This post covers the new features and enhancements that you may find beneficial.
You can download jQuery 1.4 right now, here: http://code.jquery.com/jquery-1.4.js

1. Passing Attributes to jQuery(…)

Pre 1.4, jQuery supported adding attributes to an element collection via the useful "attr" method, which can be passed both an attribute name and value, or an object specifying several attributes. jQuery 1.4 adds support for passing an attributes object as the second argument to the jQuery function itself, upon element creation.
Let's say you need to create an anchor element with several attributes. With 1.4 it's as simple as:

jQuery('<a/>', {

    id: 'foo',

    href: 'http://google.com',

    title: 'Become a Googler',

    rel: 'external',

    text: 'Go to Google!'

});

You may have noticed the "text" attribute— you'll probably be wondering what that's doing there, after all there's no "text" attribute for anchors! Well, jQuery 1.4 utilises its very own methods when you pass certain attributes. So the "text" attribute specified above would cause jQuery to call the ".text()" method, passing "Go to Google!" as its only argument.
A better example of this in action:

jQuery('<div/>', {

    id: 'foo',

    css: {

        fontWeight: 700,

        color: 'green'

    },

    click: function(){

        alert('Foo has been clicked!');

    }

});

The "id" is added as a regular attribute, but the "css" and "click" properties trigger calling of each respective method. The above code, before the 1.4 release, would have been written like this:

jQuery('<div/>')

    .attr('id', 'foo')

    .css({

        fontWeight: 700,

        color: 'green'

    })

    .click(function(){

        alert('Foo has been clicked!');

    });

2. Everything "until"!

Three new methods have been added to the DOM traversal arsenal in 1.4, "nextUntil", "prevUntil" and "parentsUntil". Each of these methods will traverse the DOM in a certain direction until the passed selector is satisfied. So, let's say you have a list of fruit:

<ul>

    <li>Apple</li>

    <li>Banana</li>

    <li>Grape</li>

    <li>Strawberry</li>

    <li>Pear</li>

    <li>Peach</li>

</ul>

You want to select all of items after "Apple", but you want to stop once you reach "Strawberry". It couldn't be simpler:

jQuery('ul li:contains(Apple)').nextUntil(':contains(Pear)');

// Selects Banana, Grape, Strawberry

3. Binding Multiple Event Handlers

Instead of chaining a bunch of event binding methods together, you can lump them all into the same call, like so:

jQuery('#foo).bind({

    click: function() {

        // do something

    },

    mouseover: function() {

        // do something

    },

    mouseout: function() {

        // do something

    }

})

This also works with ".one()".

4. Per-Property Easing

Instead of just defining one easing function for a single animation, you can now define a different easing function for each property that you're animating. jQuery includes two easing functions, swing (the default) and linear. For other ones you'll need to download them separately!
To specify an easing function for each property simply define the property as an array, with the first value being what you want to animate that property to, and the second being the easing function to use:

jQuery('#foo').animate({

    left: 500,

    top: [500, 'easeOutBounce']

}, 2000);

You can also define per-property easing functions in the optional options object as property name-value pairs in the "specialEasing" object:

jQuery('#foo').animate({

    left: 500,

    top: 500

}, {

    duration: 2000,

    specialEasing: {

        top: 'easeOutBounce'

    }

});

Editor's Note - The author of this article, James Padolsey, is being modest. This new feature was his idea!

5. New Live Events!

jQuery 1.4 adds support for delegating the "submit", "change", "focus" and "blur" events. In jQuery, we use the ".live()" method to delegate events. This is useful when you have to register event handlers on many elements, and when new elements may be added over time (using ".live()" is less-costly than re-binding continually).
But, be careful! You must use the event names, "focusin" and "focusout" if you want to delegate the "focus" and "blur" events!

jQuery('input').live('focusin', function(){

    // do something with this

});

6. Controlling a Function's Context

jQuery 1.4 provides a new "proxy" function under the jQuery namespace. This function takes two arguments, either a "scope" and a method name, or a function and the intended scope. JavaScript's "this" keyword can be quite tricky to keep a hold of. Sometimes you won't want it to be an element, but instead an object that you've previously created.
For example, here we've got an "app" object which has two properties, a "clickHandler" method and a config object:

var app = {

    config: {

        clickMessage: 'Hi!'

    },

    clickHandler: function() {

        alert(this.config.clickMessage);

    }

};

The "clickHandler" method, when called like "app.clickHandler()" will have "app" as its context, meaning that the "this" keyword will allow it access to "app". This works quite well if we simply call:

app.clickHandler(); // "Hi!" is alerted

Let's try binding it as an event handler:

jQuery('a').bind('click', app.clickHandler);

When we click an anchor it doesn't appear to work (nothing is alerted). That's because jQuery (and most sane event models) will, by default, set the context of the handler as the target element,- that is, the element that's just been clicked will be accessible via "this". But we don't want that, we want "this" to be set to "app". Achieving this in jQuery 1.4 couldn't be simpler:

jQuery('a').bind(

    'click',

    jQuery.proxy(app, 'clickHandler')

);

Now whenever an anchor is clicked, "Hi!" will be alerted!
The proxy function returns a "wrapped" version of your function, with "this" set to whatever you specify. It's useful in other contexts too, such as passing callbacks to other jQuery methods, or to plugins.

7. Delay an Animation Queue

You can now add a delay to your animation queues. In fact, this works on any queue, but its most common use case will probably be with the "fx" queue. This allows you to pause between animations without having to mess with callbacks and calls to "setTimeout". The first argument to ".delay()" is the amount of milliseconds you want to delay for.

jQuery('#foo')

    .slideDown() // Slide down

    .delay(200) // Do nothing for 200 ms

    .fadeIn(); // Fade in

If you want to delay a queue other than the default "fx" queue, then you'll need to pass the queue name as the second argument to ".delay()".

8. Check if an Element Has Something

jQuery 1.4 makes it easy to check if an element (or collection) ".has()" something. This is the programmatic equivalent to jQuery's selector filter, ":has()". This method will select all elements in the current collection that contain at least one element that complies with the passed selector.

jQuery('div').has('ul');

That would select all DIV elements that contain UL elements. In this situation you'd probably just use the selector filter (":has()"), but this method is still useful when you need to filter a collection programmatically.
jQuery 1.4 also reveals the "contains" function under the jQuery namespace. This is a low-level function that accepts two DOM nodes. It'll return a boolean indicating whether the second element is contained within the first element. E.g.

jQuery.contains(document.documentElement, document.body);

// Returns true - <body> is within <html>

9. Unwrap Elements!

We've had the ".wrap()" method for a while now. jQuery 1.4 adds the ".unwrap()" method which does the complete opposite. If we assume the following DOM structure:

<div>

    <p>Foo</p>

</div>

We can unwrap the paragraph element like so:

jQuery('p').unwrap();

The resulting DOM structure would be:

<p>Foo</p>

Essentially, this method simply removes the parent of any element.

10. Remove Elements Without Deleting Data

The new ".detach()" method allows you to remove elements from the DOM, much like the ".remove()" method. The key difference with this new method is that it doesn't destroy the data held by jQuery on that element. This includes data added via ".data()" and any event handlers added via jQuery's event system.
This can be useful when you need to remove an element from the DOM, but you know you'll need to add it back at a later stage. Its event handlers and any other data will persist.

var foo = jQuery('#foo');

// Bind an important event handler

foo.click(function(){

    alert('Foo!');

});

foo.detach(); // Remove it from the DOM

// … do stuff

foo.appendTo('body'); // Add it back to the DOM

foo.click(); // alerts "Foo!"

11. index(…) Enhancements

jQuery 1.4 gives you two new ways to use the ".index()" method. Previously, you could only pass an element as its argument and you'd expect a number to be returned indicating the index of that element within the current collection.
Passing no arguments now returns the index of an element amongst its siblings. So, assuming the following DOM structure:

<ul>

    <li>Apple</li>

    <li>Banana</li>

    <li>Grape</li>

    <li>Strawberry</li>

    <li>Pear</li>

    <li>Peach</li>

</ul>

When a list item is clicked you want to find out the index of the clicked element amongst all the other list items. It's as simple as:

jQuery('li').click(function(){

    alert( jQuery(this).index() );

});

jQuery 1.4 also allows you to specify a selector as the first argument to ".index()", doing so will give you the index of the current element amongst the collection produced from that selector.
You should note that what's returned from this method is an integer, and it will return -1 if the selector/element passed cannot be found in the document.

12. DOM Manipulation Methods Accept Callbacks

Most of the DOM manipulation methods now support passing a function as the sole argument (or second, in the case of ".css()" & ".attr()"). This function will be run on every element in the collection to determine what should be used as the real value for that method.
The following methods have this capability:

after
before
append
prepend
addClass
toggleClass
removeClass
wrap
wrapAll
wrapInner
val
text
replaceWith
css
attr
html

Within the callback function, you'll have access to the current element in the collection via "this" and its index via the first argument.

jQuery('li').html(function(i){

    return 'Index of this list item: ' + i;

});

Also, with some of the above methods you'll also get a second argument. If you're calling a setter method (like ".html()" or ".attr('href)") you'll have access to the current value. E.g.

jQuery('a').attr('href', function(i, currentHref){

    return currentHref + '?foo=bar';

});

As you can see, with the ".css()" and ".attr()" methods, you would pass the function as the second argument, since the first would be used to name the property you wish to change:

jQuery('li').css('color', function(i, currentCssColor){

    return i % 2 ? 'red' : 'blue';

});

13. Determine the Type of Object

jQuery 1.4 adds two new helper functions (stored directly under the jQuery namespace) that help you determine what type of object you're dealing with.
First, there's "isEmptyObject", this function returns a boolean indicating whether or not the the passed object is empty (devoid of properties - direct and inherited). Second, there's "isPlainObject", which will return a boolean indicating whether the passed object is a plain JavaScript object, that is, one created via "{}" or "new Object()".

jQuery.isEmptyObject({}); // true

jQuery.isEmptyObject({foo:1}); // false

jQuery.isPlainObject({}); // true

jQuery.isPlainObject(window); // false 

jQuery.isPlainObject(jQuery()); // false

Read more about: isPlainObject(…), isEmptyObject(…)

14. Closest(…) Enhancements

jQuery's ".closest()" method now accepts an array of selectors. This is useful when you want to traverse the ancestors of an element, looking for (more than one) closest elements with certain characteristics.
In addition, it now accepts a context as the second argument, meaning that you can control just how far or how close you want the DOM traversed to. Both of these enhancements accommodate rare use cases but they are used internally to great effect!
Read more about .closest(…)

15. New Events! focusIn and focusOut

As mentioned, to delegate the "focus" and "blur" events you must use these new events, called "focusin" and "focusout". These events allow you to take action when an element, or a descendant of an element, gains focus.

jQuery('form')

    .focusin(function(){

        jQuery(this).addClass('focused');

    });

    .focusout(function(){

        jQuery(this).removeClass('focused');

    });

You should also note that both of these events do not propagate ("bubble"); they are captured. This means that the outermost (ancestor) element will be triggered before the causal "target" element.

Multiple Models in a View in MVC

2014-07-23T06:21:00.002-07:00

Introduction

When I was a beginner for ASP.NET MVC, I faced a question many times: how many ways do you know to use/pass multiple models in/to a view? At that time, I knew only two ways, then I learned some other ways to achieve the same. In this article, I will share my learning so far. Hope it will be helpful for others.
Pre-requisite: you should be at intermediate level with C# and ASP.NET MVC. If you are absolute new to C# and ASP.NET MVC, please look for other resources to understand terms used here. You can put comment below article in case you need any detail. I will be happy to help. Thanks.
There are many ways of using multiple models in a view, most frequently used are given below:

ViewData
ViewBag
PartialView
TempData
ViewModel
Tuple

All the above ways of using multiple models in view have their place but we need to think and pick which one fits our requirements. All techniques have their own advantages and disadvantages.
To understand the article better, please download the attached code, have an overview of the code, then follow the steps given in this article.

Overview of Sample Demo

The attached code solution has six views demonstrating the following:

How to pass multiple models using ViewData
How to pass multiple models using ViewBag
How to pass multiple models using PartialView
How to pass multiple models using TempData
How to pass multiple models using ViewModel
How to pass multiple models using Tuple

In the sample demo, all views will have similar HTML structure to get same layout but implementation to pass models to the view will be different.
Structure of the HTML tags is shown below only code inside the scripts tag will be changed as per the scenarios.

Output of all demos will be similar to the screenshot shown below:

Creating Basic Structure of Sample Demo

Let's get started by creating a sample demo application. Follow the below steps:

Open Visual Studio 2012, select ASP.NET MVC4 Web Application template and give it project name as MultipleModelDemo and click OK. If you are using Visual Studio 2013 and MVC 5, Please look into the Update for VS 2013 / MVC 5 section below.
Select a template as Basic application then click OK. Visual Studio adds a MultipleModelDemo project in solution as shown below in screenshot.

Right click on the Models folder, add a Models.cs file. Now we need to add three models named as Course, Faculty and Student by writing the following code as shown below:

public class Course
{
    public int CourseId { get; set; }
    public string CourseName { get; set; }
}

public class Faculty
{
    public int FacultyId { get; set; }
    public string FacultyName { get; set; }
    public List<Course> AllotedCourses { get; set; }
}

public class Student
{
    public int EnrollmentNo { get; set; }
    public string StudentName { get; set; }
    public List<Course> EnrolledCourses { get; set; }
}

Add a class file under the Models folder named as Repository.cs file, which will have the implementation of methods to get hardcoded data for application in order to keep it convenient. Following is the code for GetCourse method which will return a list of courses:

public List<Course> GetCourses()
{
    return new List<Course> { 
        new Course () {  CourseId = 1, CourseName = "Chemistry"}, 
        new Course () {  CourseId = 2, CourseName = "Physics"},
        new Course () {  CourseId = 3, CourseName = "Math" },
        new Course () {  CourseId = 4, CourseName = "Computer Science" }
    };
}

Following is the code GetFaculties method which will return a list of faculties:

public List<Faculty> GetFaculties()
{
    return new List<Faculty> {                 
        new Faculty () {  FacultyId = 1, FacultyName= "Prakash",
            AllotedCourses = new List<Course> 
            {new Course () { CourseId = 1, CourseName = "Chemistry"},
                             new Course () { CourseId = 2, CourseName = "Physics"},
                             new Course () { CourseId = 3, CourseName = "Math"},
        }}, 
        new Faculty () {  FacultyId = 2, FacultyName= "Ponty" ,
            AllotedCourses = new List<Course> 
            {new Course () { CourseId = 2, CourseName = "Physics"},
                             new Course () { CourseId = 4, CourseName = "Computer Science"}
        }},
        new Faculty () {  FacultyId = 3, FacultyName= "Methu", 
            AllotedCourses = new List<Course> 
            {new Course () { CourseId = 3, CourseName = "Math"},
                             new Course () { CourseId = 4, CourseName = "Computer Science"}
        }}
    };
}

Following is the code for GetStudents method which will return a list of students:

public List<Student> GetStudents()
{
    List<Student> result = new List<Student> { 
        new Student () { EnrollmentNo = 1, StudentName= "Jim", 
            EnrolledCourses = new List<Course> 
            { new Course () { CourseId = 1, CourseName = "Chemistry"},
                              new Course () { CourseId = 2, CourseName = "Physics"},
                              new Course () { CourseId = 4, CourseName = "Computer Science"}
        }},
        
        new Student () {  EnrollmentNo = 2, StudentName= "Joli",
            EnrolledCourses = new List<Course> 
            { new Course () { CourseId = 2, CourseName = "Physics"} ,
                              new Course () 
                              { CourseId = 4, CourseName = "Computer Science"}
        }},
        
        new Student () {  EnrollmentNo = 3, StudentName= "Mortin",
            EnrolledCourses = new List<Course>
            {  new Course () { CourseId = 3, CourseName = "Math"},
                               new Course () { CourseId = 4, CourseName = "Computer Science"}
        }}
    };
    
    return result;
}

Add a HomeController to Controller folder. We will write the code in HomeController later.

In Shared folder, we will modify the existing code in _Layout.cshtml file. First write the following code in head tag:

         <head>
            <meta charset="utf-8" />
            <meta name="viewport" content="width=device-width" />           

           @*Referenced  js and css files which comes with template*@
            <script src="~/Scripts/jquery-1.8.2.min.js"></script>
            <link href="~/Content/Site.css" rel="stylesheet" />

            @*Referenced appcss file having custom CSS*@
            <link href="~/Content/appcss/appcss.css" rel="stylesheet" />    
        </head>

Write the following code in body tag:

<body>
    @* Define the place for navigation links in left side of the page*@
    <div class="navigationPanel">
        <div style="margin: 40px 25px 2px 25px;">
            <h3>Links to Demostrations</h3>
            <a href="~/Home/ViewDataDemo">ViewData Demo</a>
            <br />
            <br />
            <a href="~/Home/ViewBagDemo">ViewBag Demo</a>
            <br />
            <br />
            <a href="~/Home/PartialViewDemo">PartialView Demo</a>
            <br />
            <br />
            <a href="~/Home/TempDataDemo">TempData Demo</a>
            <br />
            <br />
            <a href="~/Home/ViewModelDemo">ViewModel Demo</a>
            <br />
            <br />
            <a href="~/Home/TupleDemo">Tuple Demo</a>
        </div>
    </div>
    <div style="float: left; margin: 25px 2px 2px 80px;">
        @RenderBody()
    </div>
</body>

So far, we have created basic code which we will be using in all scenarios. Further, we will learn each scenario one by one.

Passing Multiple Models using ViewData

ViewData is used to pass data from a controller to a view. ViewData is a dictionary of objects that is a type of ViewDataDictionary class. ViewData is defined as property in ControllerBase class. Values stored in ViewData require typecasting to their datatype in view. The values in ViewData are accessible using a key.

First, create a object of Repository class in HomeController.

Repository _repository = new Repository();

Add the following code in HomeController.

public ActionResult ViewDataDemo()
{
    ViewData["Courses"] = _repository.GetCourses();
    ViewData["Students"] = _repository.GetStudents();
    ViewData["Faculties"] = _repository.GetFaculties();
    return View();
}

Here ViewDataDemo action method will be passing all three models to its view using ViewData.

Add a view named as ViewDataDemo and write the same code as written below in body tag.

<body style="background-color: #DBDBB7">
 <h3>Passing Multiple Models using <span class="
 specialText">  <i>ViewData </i> </span> </h3>
 <table>
     <tr>
         <td class="sltCourseText">
             <h3>Select a Course  </h3>
         </td>
         <td>
             <select id="sltCourse" class="sltStyle">
                <option>Select Course </option>
                @*Iterating Course model using ViewData string as a key *@
                @foreach (var item in ViewData["Courses"] 
                as List <MultipleModelDemo.Models.Course>)
                {         
                     <option>@item.CourseName
                     </option>            
                }
             </select>
         </td>
     </tr>
 </table>
     
 <div id="facultyDetailSection">
     <h4>Faculties who teach selected course </h4>
     <div id="facultyDetailTable"> </div>
 </div>
     
 <div id="studentDetailSection">
     <h4>Students who learn selected course </h4>
     <div id="studentDetailTable"> </div>
 </div>
 </body>

Here we are iterating Course model using ViewData and casting it into a List<Course>.

Inside the body tag, add a script tag and write the following code. Here we would show the table only when user will select a valid course otherwise the facultyDetailSection and studentDetailSection should not be appearing. We are using fadeout and fadeIn function of jQuery for that purpose.

 <script>
        $(document).ready(function(){
            $("#facultyDetailSection").fadeOut(0);
            $("#studentDetailSection").fadeOut(0);
        });
        
        var selectedCourseName;
        
        $("#sltCourse").change(function () {           
            selectedCourseName = $("#sltCourse").val().trim();
            
            if (selectedCourseName === "Select Course") {
                $("#facultyDetailSection").fadeOut();
                $("#studentDetailSection").fadeOut();
            }
            else {
                getFacultyTable();
                getStudentTable();
                $("#facultyDetailSection").fadeIn();
                $("#studentDetailSection").fadeIn();
            }
        });
 </script>

Here on the change event of Course dropdown, we will read the value and confirm if there is a valid selection to display faculties and students. In case of a valid selection, getFacultyTable and getStudentTable function will be executed. Add the following functions in script tag:

    //Create table to display faculty detail
    function getFacultyTable() {         
    $("#facultyDetailTable").empty();
    $("#facultyDetailTable").append("<table id='tblfaculty'  
    class='tableStyle'><tr><th class='tableHeader' style='width:60px;'>
                                        Employee ID </th> 
                                        <th class='tableHeader'>Faculty Name 
                                        </th> </tr> </table>");

    //Get all faculties with the help of model 
    //(ViewData["Faculties"]), and convert data into json format. 
    var allFaculties = @Html.Raw(Json.Encode(ViewData["Faculties"]));

    for (var i = 0; i  < allFaculties.length; i++) {
        var allotedCourses = allFaculties[i].AllotedCourses;
        for (var j = 0; j  < allotedCourses.length; j++) {
            if(allotedCourses[j].CourseName === selectedCourseName)
                $("#tblfaculty").append
                (" <tr> <td class='tableCell'>"  + 
                allFaculties[i].FacultyId 
                    + " </td> <td class='tableCell'>"+
                    allFaculties[i].FacultyName+" </td> </tr>");
        }
    }
}

//Create table to display student detail
function getStudentTable() {
    $("#studentDetailTable").empty();
    $("#studentDetailTable").append(" <table id='tblStudent' 
    class='tableStyle'> <tr> <th class='tableHeader' style='width:60px;'>
                                        Roll No </th> <th 
                                        class='tableHeader'>Student Name 
                                        </th> </tr> </table>");

    //Get all students with the help of model 
    //(ViewData["Students"]), and convert data into json format. 
    var allStudents = @Html.Raw(Json.Encode(ViewData["Students"]));

    for (var i = 0; i  < allStudents.length; i++) {
        var studentCourses = allStudents[i].EnrolledCourses;
        for (var j = 0; j  < studentCourses.length; j++) {
            if(studentCourses[j].CourseName === selectedCourseName)                      
                $("#tblStudent").append(" <tr> 
                <td class='tableCell'>"  + allStudents[i].EnrollmentNo 
                    + " </td> <td  class='tableCell'>
                    "+allStudents[i].StudentName+" </td> </tr>");
        }
    }           
}

Note: As we have mentioned, all view will have same layout so further demos will have almost the same code as you have written in body tag of ViewDataDemo.cshtml file, now in further demos we just need to modify foreach function to fill data in dropdown and two lines of code in getFacultyTable and getStudentTable JavaScript function.

Passing Multiple Models using ViewBag

ViewBag is also used to pass data from a controller to a view. It is a dynamic property which comes in ControllerBase class that is why it doesn’t require typecasting for datatype.

Add the following code in HomeController:

public ActionResult ViewBagDemo()
{
    ViewBag.Courses = _repository.GetCourses();
    ViewBag.Students = _repository.GetStudents();
    ViewBag.Faculties = _repository.GetFaculties();
    return View();
}

Here ViewBagDemo action method will be passing data to view (ViewBagDemo.cshtml) file using ViewBag.

Add a view named as ViewBagDemo. All code will be same as you have written in ViewDataDemo.cshtml file. Just modify input model to foreach function.

@*Iterating Course model using ViewBag *@
@foreach (var item in ViewBag.Courses)
{         
    <option>@item.CourseName</option>            
}

In script tag, replace the following line of code in getFacultyTable function:

//Get all faculties with the help of model 
// (ViewBag.Faculties), and convert data into json format.                
var allFaculties = @Html.Raw(Json.Encode(ViewBag.Faculties));

Replace the following line of code in getStudentTable function:

//Get all students with the help of model(ViewBag.Students), 
//and convert data into json format.
var allStudents = @Html.Raw(Json.Encode(ViewBag.Students));

Passing Multiple Models using PartialView

Partial view is used where you need to share the same code (Razor and HTML code) in more than one view. For more details about PartialView, please visit here.

In Home controller, add the following code, PartialViewDemo action method will return a view having the list of all courses only. This action method will not have or pass any faculty or student information as of now.
```
public ActionResult PartialViewDemo()
{
    List<Course> allCourse = _repository.GetCourses();
    return View(allCourse);
}            
```

Add a view named as PartialViewDemo. All HTML code will be same as you have written before. Just modify foreach function.

@*Iterating Course Model*@
@foreach(var item in Model)
{         
    <option>@item.CourseName
    </option>            
}

In script tag, modify getFacultyTable function as written below:

function getFacultyTable() {
  $.ajax({
         // Get Faculty PartialView
         url: "/Home/FacultiesToPVDemo",
     type: 'Get',
     data: { courseName: selectedCourseName },
     success: function (data) {
        $("#facultyDetailTable").empty().append(data);
     },
     error: function () {
        alert("something seems wrong");
 }
  });
}

Modify getStudentTable function as written below:

    function getStudentTable() {
    $.ajax({
        // Get Student PartialView
        url: "/Home/StudentsToPVDemo",
        type: 'Get',
        data: { courseName: selectedCourseName },
        success: function (data) {
            $("#studentDetailTable").empty().append(data);
        },
        error: function () {
            alert("something seems wrong");
        }
    });
}

Add a new Action method in HomeController as StudentsToPVDemo and add the following code in StudentsToPVDemo action method.

public ActionResult StudentsToPVDemo(string courseName)
{
    IEnumerable <Course> allCourses = _repository.GetCourses();
    var selectedCourseId = (from c in allCourses where 
    c.CourseName == courseName select c.CourseId).FirstOrDefault();
    
    IEnumerable <Student> allStudents = _repository.GetStudents();
    var studentsInCourse = allStudents.Where(s => 
    s.EnrolledCourses.Any(c => c.CourseId == selectedCourseId)).ToList();
    
    return PartialView("StudentPV", studentsInCourse); 
}

Add a PartialView to the Shared folder by right clicking on StudentsToPVDemo action method, give it name as StudentPV. StudentsToPVDemo action will return StudentPV PartialView having the list of students studying in a particular course.

Add the following code in StudentPV.cshtml file.

@model  IEnumerable <MultipleModelDemo.Models.Student>
 <table id="tblFacultyDetail" class="tableStyle">
         <tr>
         <th class="tableHeader" style="width:60px;">Roll No </th>
         <th class="tableHeader">Student Name </th>
         </tr>
    @foreach (var item in Model)
    {
          <tr>
             <td  class="tableCell" >@item.EnrollmentNo </td>
             <td class="tableCell">@item.StudentName </td>
         </tr>
    }       
 </table>

Add a new action method to call PatialView for faculties in HomeController. Name it as FacultiesToPVDemo and add the following code:

public ActionResult FacultiesToPVDemo(string courseName)
{
    IEnumerable <Course> allCourses = _repository.GetCourses();
    var selectedCourseId = (from c in allCourses where 
    c.CourseName == courseName select c.CourseId).FirstOrDefault();
    
    IEnumerable <Faculty> allFaculties = _repository.GetFaculties();
    var facultiesForCourse = allFaculties.Where(f => 
    f.AllotedCourses.Any(c =>  c.CourseId == selectedCourseId)).ToList();
    
    return PartialView("FacultyPV", facultiesForCourse);
  }

Add a PartialView named as FacultyPV as we did for student PartialView, write the same code as you have written in StudentPV.cshtml file. Just replace one line of code as:
```
@model  IEnumerable<MultipleModelDemo.Models.Faculty>
```
FacultiesToPVDemo action will return FacultyPV PartialView having the list of faculties who teach a particular course.

Passing Multiple Models using TempData

TempData is a dictionary of objects that is a type of TempDataDictionary class. TempData is defined as property in ControllerBase class. Values stored in TempData require typecasting to datatype in view. The values in TempData are accessible using a key. It is similar to ViewData but the difference is that it allow us to send and receive the data from one controller to another controller and from one action to another action. It’s all about possible because it internally uses session variables.
For more information about TempData, please visit here. Here, we will use TempData only to hold (at server side HomeController) and pass (to the TempDataDemo.cshtml) List of Courses.

In home controller, add the following code:

public ActionResult TempDataDemo()
{
    // TempData demo uses repository to get List<courses> only one time
    // for subsequent request to get List<courses> it will use TempData
    TempData["Courses"] = _repository.GetCourses();

    // This will keep Courses data untill next request is served
    TempData.Keep("Courses");
    return View();
}

Using TempData, we can pass values from one action to another action. TempData["Courses"] having the list of course. We will access this list in FacultiesToTempDataDemo action as shown below:

public ActionResult FacultiesToTempDataDemo(string courseName)
{
    var allCourses = TempData["Courses"] as IEnumerable <Course>;
    
    // Since there are two AJAX call on TempDataPage
    // So we keep to keep Courses data for the next one
    TempData.Keep("Courses");
    var selectedCourseId = (from c in allCourses where 
    c.CourseName == courseName select c.CourseId).FirstOrDefault();
    
    IEnumerable <Faculty> allFaculties = _repository.GetFaculties();
    var facultiesForCourse = allFaculties.Where(f => 
    f.AllotedCourses.Any(c => c.CourseId == selectedCourseId)).ToList();
    
    return PartialView("FacultyPV", facultiesForCourse);
}

public ActionResult StudentsToTempDataDemo(string courseName)
{
    var allCourses = TempData["Courses"] as IEnumerable <Course>;
    
    // If there is change in course again...it may cause more AJAX calls
    // So we need to keep Courses data
    TempData.Keep("Courses");
    
     var selectedCourseId = (from c in allCourses where 
     c.CourseName == courseName select c.CourseId).FirstOrDefault();
     
    IEnumerable <Student> allStudents = _repository.GetStudents();
    var studentsInCourse = allStudents.Where(s => 
    s.EnrolledCourses.Any(c => c.CourseId == selectedCourseId)).ToList();
    
    return PartialView("StudentPV", studentsInCourse);
}

Add a view by right clicking on TempDataDemo action method. Write the same code as you have written in PartialViewDemo.cshtml. Only one line of code needs to modify as written below:
```
@*Iterating Course model using TempData["Courses"] *@
@foreach (var item in TempData["Courses"] 
 as List <MultipleModelDemo.Models.Course>)
{         
    <option>@item.CourseName </option>            
}           
```
Modify url in getFacultyTable and getStudentTable function respectively as written below:
```
url: "/Home/FacultiesToTempDataDemo",
url: "/Home/StudentsToTempDataDemo",            
```
Both Action methods FacultiesToTempDataDemo and StudentsToTempDataDemo will return the same PartialView which we used for PartialView demo.

Passing Multiple Models using ViewModel

ViewModel is a pattern that allow us to have multiple models as a single class. It contains properties of entities exactly need to be used in a view. ViewModel should not have methods. It should be a collection of properties needed for a view.

We have three models (classes) named as Student, Course and Faculty. All are different models but we need to use all three models in a view. We will create a ViewModel by adding a new folder called ViewModels and add a class file called ViewModelDemoVM.cs and write the following code as shown below:
```
public class ViewModelDemoVM
{        
    public List <Course> allCourses { get; set; }
    public List <Student> allStudents { get; set; }
    public List <Faculty> allFaculties { get; set; }
}            
```
Note: As a good practice when you create any ViewModel, it should have suffix as VM or ViewModel.

In the HomeController, add the following code:

public ActionResult ViewModelDemo()
{
    ViewModelDemoVM vm = new ViewModelDemoVM();
    vm.allCourses = _repository.GetCourses();
    vm.allFaculties = _repository.GetFaculties();
    vm.allStudents = _repository.GetStudents();

    return View(vm);
}

ViewModelDemo is an action method that will return a view having ViewModelDemoVM which has lists of all Courses, Faculties and Students.

Right click on ViewModelDemo to add a view is called ViewModelDemo. ViewModelDemo.cshtml view will use ViewModelDemoVM as Model as shown below:
```
@model MultipleModelDemo.ViewModel.ViewModelDemoVM            
```

Modify foreach function.

@*Iterating Course ViewModel *@
@foreach (var item in Model.allCourses)
    {         
        <option>@item.CourseName</option>            
    }

Replace the following line of code in getFacultyTable function:

//Get all faculties with the help of viewmodel
//(Model.allFaculties), and convert data into json format.
var allFaculties = @Html.Raw(Json.Encode(Model.allFaculties));

Replace the following line of code in getStudentTable function:

//Get all students with the help of viewmodel(Model.allStudents), 
//and convert data into json format.
var allStudents = @Html.Raw(Json.Encode(Model.allStudents));

Passing Multiple Models using Tuple

Tuple is a new class introduced in .NET Framework 4.0. It is an ordered sequence, immutable, fixed-size collection of heterogeneous (allows us to group multiple kind of data types) objects.

Add the following code in Home controller.

public ActionResult TupleDemo()
{
    var allModels = new Tuple <List <Course>, 
    List <Faculty>,  List <Student>>
    (_repository.GetCourses(), _repository.GetFaculties(),  _repository.GetStudents()) { };
     return View(allModels);
}

Here, we are defining a tuple which is having lists of courses, faculties and students. We are passing this tuple to the View.

Add a View named as TupleDemo. Write code as you have written in ViewModelDemo.cshtml file. Just need to replace few lines of code. Replace model declarations as shown below. Here, we will use the namespace used to avoid long fully qualified class names.
```
@using MultipleModelDemo.Models;
@model Tuple <List <Course>, List <Faculty>, List <Student>>            
```

Modify foreach function:

@*Iterating Course model using tuple *@
@foreach (var item in Model.Item1)
    {         
         <option>@item.CourseName </option>            
    }

Here Model.Item1 is mapped to Course model.

Inside the JavaScript function called getFacultyTable replace the following line of code:
```
var allFaculties = @Html.Raw(Json.Encode(Model.Item2));            
```
Here Model.Item2 is mapped with Faculty model.
Inside the JavaScript function called getStudentTable, replace the following line of code:
```
var allStudents = @Html.Raw(Json.Encode(Model.Item3));            
```
Here Model.Item3 is mapped with Student model.

Update for VS 2013 / MVC 5

If you would like to use Visual Studio 2013 / MVC 5, Step 1 and 2 as given for MVC 4 would be different, So please follow the steps as given below and then start from steps 3 as given for MVC 4 above.

Open Visual Studio 2013, Click on "New Project" and select ASP.NET Web Application template and give it project name as MultipleModelDemo and click OK.
Select a template as MVC and make sure that all check box given in lower section of popup are unchecked other than MVC. Before clicking OK, we need to change Authentication (since for this demo we are not using either Authentication or Unit Tests to keep it simple and to the point). Please find screen shots below for the same:

Changing the Authentication from "Individual User Account" to "No Authentication":

Visual Studio adds a MultipleModelDemo project in solution. Now you can follow the step 3 and further as given for MVC 4.

Conclusion

In this article, we learned how to use multiple models in a view. In the article How to Choose the Best Way to Pass Multiple Models, I have shared my findings about when and where to pick a particular way to use multiple models in a view. Your inputs and queries are most welcome. Thanks.

Tuples in DotNet

2014-07-23T06:18:00.003-07:00

Tuples are not new to software engineering. But ofcource it's new to C#. C# has introduced as a Static programming language where tuples were applicable to dynamic programming languages. What's this Static and Dynamic programming languages. There are dynamic and static programming languages. In a dynamic language, such as Perl or LISP, a developer can create variables without specifying their type. This creates more flexible programs and can simplify prototyping and some object-oriented coding. In a static programming language, such as C or C#, a developer must declare the type of each variable before the code is compiled, making the coding less flexible, but also less error-prone. But in static programming scenario too we have scenarios where tuples can reduce the effort and avoid unwanted lines of code. The latest functional programming language from Microsoft, F# also supports tuples in a far better syntax. Let me explain the tuples world in a C# 4.0 scenario. I hope you already downloaded the attached solution.

The main purpose of tuples introduction in .NET4.0 are based on below needs which were not available till .NET 3.5 and now can be handled with tuples.

Developers using used KeyValuePair{TKey,TValue} just to hold a pair of values together. i.e. only 2 dependent values, but using a type which is meant to store more number of items
Anonymous types cannot be passed out of the method
Need to pass multiple out references to a method, if we needed multiple values from a method. Otherwise declaring a full class and defining properties to return that type from the method.

Above are the scenarios faced till 4.0. How we can tackle these in 4.0 using tuples? Just go through each method in my uploaded code.

1. Method returning 2 values with tuples

private Tuple<string, string> GetFandLNames(string name)

{

Tuple<string, string> flNames = null;

string[] names = name.Split(',');

flNames = Tuple.Create<string, string>(names[0], names[1]);

return flNames;

}

As you can see we are not using any out parameters. Tuples can be created 2 ways i.e. either using new key word just like creating any object or using static method of Create. Here I used Create. You also need to mention the types exists in side tuple as I mentioned 2 string types which carries first name and last name. Then the method returns the tuple which carries the required first name and last name. Now how we can retrieve the values from tuple? It's using properties. If you have 2 items inside a tuple, you will have 2 properties name "Item1" and "Item2" like below screen shot.

2. Method returning 2 values of different types using tuples

Here explaining tuples which carrying 2 different types rather than same data type. Below is the method which is returning tuple of 2 different typed i.e. Date and int.

private Tuple<DateTime, int> GetDOBAge()

{

Tuple<DateTime, int> flNames = null;

flNames = Tuple.Create<DateTime, int>(new DateTime(1973,5,22),30);

return flNames;

}

Values are retrieving same manner as like above. But this time the properties Item1 and Item2 are of different data types.

3. Method returning custom information using Dictionary

private Tuple<Dictionary<int,string>, Dictionary<int,string>> GetEmployeeDetails()

{

Dictionary<int, string> emp = new Dictionary<int, string>();

emp.Add(1, "Jaish");

emp.Add(2, "Ramji");

emp.Add(3, "Vulise");

Dictionary<int, string> dept = new Dictionary<int, string>();

dept.Add(1, "Dev");

dept.Add(2, "Sales");

dept.Add(3, "Test");

Tuple<Dictionary<int, string>, Dictionary<int, string>> empDetails = new Tuple<Dictionary<int, string>, Dictionary<int, string>>(emp, dept);

return empDetails;

}

Above method contains employee and department details. It returns all those details as a single tuple. This tuple contains 2 dictionary types. More over for you people I made this tuple creation using new key word, just for a change. Below explaining the code to iterate through each items in this case.

Tuple<Dictionary<int, string>, Dictionary<int, string>> empDetails = GetEmployeeDetails();

foreach (KeyValuePair<int, string> keyValue in empDetails.Item1)

{

MessageBox.Show("ID :" + keyValue.Key + Environment.NewLine + "Name :" + keyValue.Value);

}

foreach (KeyValuePair<int, string> keyValue in empDetails.Item2)

{

MessageBox.Show("ID :" + keyValue.Key + Environment.NewLine + "Dept :" + keyValue.Value);

}

This time Item1 and Item2 contains more information in the form of Dictionary.

4. How many items can keep in side Tuples

When you check the Tuple, you can see only 8 items are supporting using overriding like below screen shot.

Then how about more numbers? If we need more than 8 items to be kept inside a tuple, we need to care about the last parameter in above screen shot which saying "TRest". We will replace this RTest with another tuple which again can carry 8 items so on. Below is a simple example which is storing 9 numbers in a tuple by replacing the 8th parameter with another new tule.

Tuple<int, int, int, int, int, int, int, Tuple<int, int>> tup = new Tuple<int, int, int, int, int, int, int, Tuple<int, int>>(1, 2, 3, 4, 5, 6, 7, new Tuple<int, int>(8, 9));

Summary

The .NET Framework 4 provides the System.Tuple class for creating tuple objects that contain structured data. It also provides generic tuple classes to support tuples that have from one to eight components (that is, singletons through octuples). To support tuple objects that have nine or more components, there is a generic tuple class with seven type parameters and an eighth parameter of any tuple type.

Intellisense for jQuery

2014-07-23T06:17:00.005-07:00

Problem

In my programming environment I have strong support for code-completion through IntelliSense. I would like the same feature when I'm working with the jQuery library.

Solution

Visual Studio 2008 SP1 and Visual Studio 2010 use formatted comments in JavaScript source files in a very similar fashion to c# and VB.NET. By leveraging readily available commented versions of the jQuery library you'll get the full-featured power of IntelliSense.

Don't have a documentation file? Even without the specialized commenting IntelliSense works with library references to give you a rich set of features such as code-completion and method signature information.

Additionally, you can learn to apply comments to expose summary and parameter information for the code in your own libraries.

The Goal

What we're looking for is pretty straightforward. Basically, we want to see object members, code-completion and parameter information. It should look something like this:

This is achieved by including a special version of jQuery in our project. You will need to download a copy of this documention from the jQuery web site, listed as "Visual Studio" in the Documentation section of the downloads. The downloaded file name will include "vsdoc", as in "Visual Studio Documentation", in it's name.

Grab a copy of the file and add it to your project, saving it in the same directory as the jQuery library.

Enabling IntelliSense in a Web Form or View Page

Remeber, you can get most of IntelliSense's features (code completion, limited parameter information) even when the file you reference does not have a commented version available. But, once you've put a properly-formatted VSDoc file in the same directory as the jQuery library you've done all you need to do to get all aspects of the tool. The rest is up to Visual Studio.

Visual Studio opportunistically searches for documentation files (and debug versions of your libraries) in the same directory as any script you've referenced. Following a naming convention with the name of a library as a root, for example jquery-1.4.1.js, the IDE will search for:

jquery-1.4.1-vsdoc.js, then if the IDE can't find it will search for...
jquery-1.4.1.debug.js, then if the IDE can't find it will search for...
jquery-1.4.1.js

These files are sought out for any script reference you make, be it as standard HTML script tags, in ASP.NET Script Manager and Script Manager Proxy tags, as well as in XML comment references (which we'll see in a moment).

This makes it easy for any developers who already have debug versions of their scripts with the "dot debug" convention. By keeping the VSDoc or DEBUG files next to your runtime version you give the IDE everything it needs to serve up some IntelliSense coolness.

Enabling IntelliSense in a Script

You can take advantage of the same great feature in script files, too. The idea is the same, but the markup is a little simpler; it is achieved through XML comment references:

/// <reference path="jquery-1.4.1.js" />

That one line at the top of a stand-alone JavaScript file is all you need, provided the VSDoc file is in the same directory.

Visual Studio 2010, IntelliSense and the CDN

We'll shift gears here quickly and talk about Content Delivery Networks, or CDNs. CDNs are made up of multiple servers, positioned at critical sites world wide. These servers all host the same set of files, allowing the closest server to the user respond to the request for a given file. CDNs reduce the amount of traffic on the internet by serving content locally with the added benefit of increasing the performance of downloads for users.

Why is this relevant to IntelliSense and Visual Studio 2010? With the latest version of the IDE you are now able reference files that are not located locally, i.e., that are out on the network somewhere, including on a CDN.

Have a look at how you can do this with the jQuery library:

<script src="http://ajax.microsoft.com/ajax/jquery/jquery-1.4.1.min.js" type="text/javascript">
</script>

Let's consider some of the immediate benefits gained by this feature of VS 2010:

you get the same opportunistic VSDoc and DEBUG file searching from the cloud and don't have to download the documentation files
you don't have to download or deploy the library itself
you will likely improve the download speed of your web page for users
some CDNs will automatically serve the latest copy of a script if you omit the revision number, meaning your pages will benefit from performance or security upgrades as they become available

Again, Visual Studio 2008 SP1 will not grab the files off the network; however it is able to grab VSDoc and DEBUG files from the local file system.

Getting IntelliSense for Your Script Files

Excellent, so we're humming along with jQuery and - in Visual Studio 2010 - we're able to take advantage of IntelliSense from files even if they live in the cloud, but eventually we're going to have to write our own code too, right?

So, how do we get IntelliSense for our own libraries?

Let's examine the following script:

function Shape(sides) {
this.numsides = sides;
this.ShowSides = function () { alert(this.numsides) };
}
Shape.prototype.AddSide = function () {
this.numsides += 1;
}

Let's assume the code above is stored in a file called shapes.js and that we have it referenced in the source file we're working on, as we did with the jQuery library. With no extra effort we get code completion and some hinting about the method's parameters.

We see member variables, methods defined through closure as well as through the prototype, and this is all free. To take it to the next level we're going to have to resort to a trick we've been using for years in Visual Studio with a syntax meant for documentation.

Consider the revised script:

view plaincopy to clipboardprint?

function Shape(sides) {
/// <summary>Creates a new shape with the number of sides specified.</summary>
/// <param name="sides" type="integer">The number of sides for a shape.</param>
this.numsides = sides;
this.ShowSides = function () {
/// <summary>Alerts the user to the current number of sides on the shape.</summary>
alert(this.numsides)
};
}
Shape.prototype.AddSide = function () {
/// <summary>Adds a side to the shape.</summary>
this.numsides += 1;
}

With a set of triple slashes and some XML style comments, we can now unleash IntelliSense on our code with full force:

For a complete breakdown of how to fully comment your library see this post by Bertrand Le Roy.

Wrapping Up

IntelliSense is a feature that just keeps getting better in every release of Visual Studio. Over the years it has evolved from it's humble beginnings adding features, additional languages, pre-compilation support, richer interaction from within the IDE, and now even support for files in the cloud. It's likely something that you use already, so you'll be glad to see such strong support for jQuery with this excellent tool.

MVC Interview Questions

2014-07-14T02:52:00.003-07:00

Introduction

This article provides some interview questions and answers of MVC, basically covering most of MVC 2, MVC 3 and MVC 4 topics that are more likely to be asked in job interviews/tests/exams.

The sole purpose of this article is to sum up important questions and answers that can be used by developers to brush-up on MVC before they go to an interview including it.

What is MVC?

MVC is a framework pattern that splits an application's implementation logic into three component roles: models, views, and controllers.

Model: The business entity on which the overall application operates. Many applications use a persistent storage mechanism (such as a database) to store data. MVC does not specifically mention the data access layer because it is understood to be encapsulated by the Model.

View: The user interface that renders the Model into a form of interaction.

Controller: Handles a request from a View and updates the Model that results in a change of the Model's state.

To implement MVC in .NET we need mainly three classes (View, Controller and the Model).

Explain MVC Architecture?

The architecture is self-explanatory. The browser (as usual) sends a request to IIS, IIS searches for the route defined in the MVC application and passes the request to the controller as specified by the route, the controller communicates with the model and passes the populated model (entity) to View (front end), Views are populated with model properties, and are rendered on the browser, passing the response to the browser through IIS via controllers that invoked the specified View.

What are the new features of MVC 2?

ASP.NET MVC 2 was released in March 2010. Its main features are:

Introduction of UI helpers with automatic scaffolding with customizable templates.

Attribute-based model validation on both client and server.

Strongly typed HTML helpers.

Improved Visual Studio tooling.

There were also many API enhancements and "pro" features, based on feedback from developers building a variety of applications on ASP.NET MVC 1, such as:

Support for partitioning large applications into areas.

Asynchronous controllers support.

Support for rendering subsections of a page/site using Html.RenderAction.

Many new helper functions, utilities, and API enhancements.

What are the new features of MVC 3?
ASP.NET MVC 3 shipped just 10 months after MVC 2 in Jan 2011. Some of the top features in MVC 3 included:

The Razor view engine.

Support for .NET 4 Data Annotations.

Improved model validation

Greater control and flexibility with support for dependency resolution and global action filters.

Better JavaScript support with unobtrusive JavaScript, jQuery Validation, and JSON binding.

Use of NuGet to deliver software and manage dependencies throughout the platform.

What are the new features of MVC 4?

The following are the top features of MVC 4:

ASP.NET Web API.

Enhancements to default project templates.

Mobile project template using jQuery Mobile.

Display Modes.

Task support for Asynchronous Controllers.

Bundling and minification.

Explain "page lifecycle" of ASP.NET MVC

The following processes are performed by ASP.NET MVC page::

App initialization

Routing

Instantiate and execute controller

Locate and invoke controller action

Instantiate and render view

Advantages of MVC Framework

Provides a clean separation of concerns among UI (Presentation layer), model (Transfer objects/Domain Objects/Entities) and Business Logic (Controller).

Easy to UNIT Test.

Improved reusability of views/model. One can have multiple views that can point to the same model and vice versa.

Improved structuring of the code.

What is meant by Separation of Concerns?

As per Wikipedia 'the process of breaking a computer program into distinct features that overlap in functionality as little as possible'. The MVC design pattern aims to separate content from presentation and data-processing from content.

Where do we see Separation of Concerns in MVC?
Between the data-processing (Model) and the rest of the application.

When we talk about Views and Controllers, their ownership itself explains separate. The views are just the presentation form of an application, it does not need to know specifically about the requests coming from the controller. The Model is independent of View and Controllers, it only holds business entities that can be passed to any View by the controller as required for exposing them to the end user. The controller is independent of Views and Models, its sole purpose is to handle requests and pass it on as per the routes defined and as per the need of rendering the views. Thus our business entities (model), business logic (controllers) and presentation logic (views) lie in logical/physical layers independent of each other.

What is Razor View Engine?

Razor is the first major update to render HTML in MVC 3. Razor was designed specifically as a view engine syntax. It has one main focus: code-focused templating for HTML generation. Here's how that same markup would be generated using Razor:@model MvcMusicStore.Models.Genre@{ViewBag.Title = "Browse Albums";}<div class="genre"><h3><em>@Model.Name</em> Albums</h3><ul id="album-list">@foreach (var album in Model.Albums)
{<li>
<a href="@Url.Action("Details", new { id = album.AlbumId })"><img alt="@album.Title" src="@album.AlbumArtUrl" /><span>@album.Title</span></a>
</li>}</ul>
</div>

The Razor syntax is easier to type, and easier to read. Razor doesn't have the XML-like heavy syntax of the Web Forms view engine.

What is Unobtrusive JavaScript?
Unobtrusive JavaScript is a general term that conveys a general philosophy, similar to the term REST (Representational State Transfer). The high-level description is that unobtrusive JavaScript doesn't intermix JavaScript code in your page markup. For example, rather than hooking in via event attributes like onclick and onsubmit, the unobtrusive JavaScript attaches to elements by their ID or class, often based on the presence of other attributes (such as HTML5 data-attributes).

It's got semantic meaning and all of it; the tag structure, element attributes and so on should have a precise meaning. Strewing JavaScript gunk across the page to facilitate interaction (I'm looking at you, -doPostBack!) harms the content of the document.

What is JSON Binding?

MVC 3 included JavaScript Object Notation (JSON) binding support via the new JsonValueProviderFactory, enabling the action methods to accept and model-bind data in JSON format. This is especially useful in advanced Ajax scenarios like client templates and data binding that need to post data back to the server.

What is Dependency Resolution?
MVC 3 introduced a new concept called a dependency resolver, that greatly simplified the use of dependency injection in your applications. This made it easier to decouple application components, making them more configurable and easier to test.

Support was added for the following scenarios:

Controllers (registering and injecting controller factories, injecting controllers)

Views (registering and injecting view engines, injecting dependencies into view pages)

Action filters (locating and injecting filters)

Model binders (registering and injecting)

Model validation providers (registering and injecting)

Model metadata providers (registering and injecting)

Value providers (registering and injecting)

What are Display Modes in MVC 4?
Display modes use a convention-based approach to allow selecting various views based on the browser making the request. The default view engine first looks for views with names ending with ".Mobile.cshtml" when the browser's user agent indicates a known mobile device. For example, if we have a generic view titled "Index.cshtml" and a mobile view titled "Index.Mobile.cshtml" then MVC 4 will automatically use the mobile view when viewed in a mobile browser.

Additionally, we can register your own custom device modes that will be based on your own custom criteria, all in just one code statement. For example, to register a WinPhone device mode that would serve views ending with ".WinPhone.cshtml" to Windows Phone devices, you'd use the following code in the Application_Start method of your Global.asax:DisplayModeProvider.Instance.Modes.Insert(0, new DefaultDisplayMode("WinPhone")
{ContextCondition = (context => context.GetOverriddenUserAgent().IndexOf
("Windows Phone OS", StringComparison.OrdinalIgnoreCase) >= 0)});
What is AuthConfig.cs in MVC 4?

"AuthConfig.cs" configures security settings, including sites for OAuth login.

What is BundleConfig.cs in MVC 4?

"BundleConfig.cs" in MVC4 registers bundles used by the bundling and minification system. Several bundles are added by default, including jQuery, jQueryUI, jQuery validation, Modernizr, and default CSS references.

What is FilterConfig.cs in MVC 4?

This is used to register global MVC filters. The only filter registered by default is the HandleErrorAttribute, but this is a great place to put other filter registrations.

What is RouteConfig.cs in MVC 4?

"RouteConfig.cs" holds the granddaddy of the MVC config statements and Route configuration.

What is WebApiConfig.cs in MVC 4?

Used to register Web API routes, as well as set any additional Web API configuration settings.

What's new for adding a controller in a MVC 4 application?

Previously (in MVC 3 and MVC 2), the Visual Studio Add Controller menu item only displayed when we right-clicked on the Controllers folder. However, the use of the Controllers folder was purely for organization. (MVC will recognize any class that implements the IController interface as a Controller, regardless of its location in your application.) The MVC 4 Visual Studio tooling has been modified to display the Add Controller menu item for any folder in your MVC project. This allows us to organize controllers however you would like, perhaps separating them into logical groups or separating MVC and Web API controllers.

What are the software requirements of an ASP.NET MVC 4 application?

MVC 4 runs on the following Windows client operating systems:

Windows XP

Windows Vista

Windows 7

Windows 8

It runs on the following server operating systems:

Windows Server 2003

Windows Server 2008

Windows Server 2008 R2

MVC 4 development tooling is included with Visual Studio 2012 and can be installed on Visual Studio 2010 SP1/Visual Web Developer 2010 Express SP1.

What are the various types of Application Templates used to create an MVC application?

The various templates are as follows:

The Internet Application template: This contains the beginnings of an MVC web application, enough that you can run the application immediately after creating it
and see a few pages. This template also includes some basic account management functions that run against the ASP.NET Membership.

The Intranet Application template: The Intranet Application template was added as part of the ASP.NET MVC 3 Tools Update. It is similar to the Internet Application template, but the account management functions run against Windows accounts rather than the ASP.NET Membership system.

The Basic template: This template is pretty minimal. It still has the basic folders, CSS, and MVC application infrastructure in place, but no more. Running an application created using the Empty template just gives you an error message.

Why use Basic template? The Basic template is intended for experienced MVC developers who want to set up and configure things exactly how they want them.

The Empty template: The Basic Template was previously called the Empty Template, but developers complained that it wasn't quite empty enough. With MVC 4, the previous Empty
Template was renamed Basic, and the new Empty Template is about as empty as possible.

It has the assemblies and basic folder structure in place, but that's about it.

The Mobile Application template: The Mobile Application template is preconfigured with jQuery Mobile to jump-start creating a mobile only website. It includes mobile visual themes, a touch-optimized UI, and support for Ajax navigation.

The Web API template: The ASP.NET Web API is a framework for creating HTTP services.

The Web API template is similar to the Internet Application template but is streamlined for Web API development. For instance, there is no user account management functionality, since Web API account management is often significantly different from standard MVC account management. Web API functionality is also available in the other MVC project templates, and even in non-MVC project types.

What are the default Top-level directories created when adding a MVC 4 application?
The default Top-level directories are:

/Controllers: For Controller classes that handle URL requests

/Models: For classes that represent and manipulate data and business objects

/Views: For UI template files that are responsible for rendering output like HTML

/Scripts: For JavaScript library files and scripts (.js)

/Images: For images used in your site

/Content: For CSS and other site content, other than scripts and images

/Filters: For code filters

/App_Data: To store data files you want to read/write

/App_Start: For configuration code of features like Routing, Bundling, Web API.

What is namespace of ASP.NET MVC?

ASP.NET MVC namespaces as well as classes are located in assembly System.Web.Mvc.

Note: Some of the content has been taken from various books/articles.

What is System.Web.Mvc namespace?
This namespace contains classes and interfaces that support the MVC pattern for ASP.NET Web applications. This namespace includes classes that represent controllers, controller
factories, action results, views, partial views, and model binders.

What is System.Web.Mvc.Ajax namespace?

The System.Web.Mvc.Ajax namespace contains classes that support Ajax scripting in an ASP.NET MVC application. The namespace includes support for Ajax scripts and Ajax option settings as well.

What is System.Web.Mvc.Async namespace?

The System.Web.Mvc.Async namespace contains classes and interfaces that support asynchronous actions in an ASP.NET MVC application.

What is System.Web.Mvc.Html namespace?

The System.Web.Mvc.Html namespace contains classes that help render HTML controls in an MVC application. This namespace includes classes that support forms, input controls, links, partial views, and validation.

What is ViewData, ViewBag and TempData?
MVC provides ViewData, ViewBag and TempData for passing data from the controller, view and in subsequent requests as well. ViewData and ViewBag are similar to some extent but TempData performs additional roles.

What are the roles and similarities between ViewData and ViewBag?

Maintains data when moving from controller to view.

Passes data from the controller to the respective view.

Their value becomes null when any redirection occurs, because their role is to provide a way to communicate between controllers and views. It's a communication mechanism within the server call.

What are the differences between ViewData and ViewBag (taken from a blog)?

ViewData is a dictionary of objects derived from the ViewDataDictionary class and accessible using strings as keys.

ViewBag is a dynamic property that takes advantage of the new dynamic features in C# 4.0.

ViewData requires typecasting for complex data types and checks for null values to avoid error.

ViewBag doesn't require typecasting for complex data types.

NOTE: Although there might not be a technical advantage to choosing one format over the other, there are some critical differences to be aware of between the two syntaxes.
One obvious difference is that ViewBag works only when the key being accessed is a valid C# identifier. For example, if you place a value in ViewData["KeyWith Spaces"] then you can't access that value using ViewBag because the code won't compile.

Another key issue to be aware of is that dynamic values cannot be passed in as parameters to extension methods. The C# compiler must know the real type of every parameter at compile time in order for it to choose the correct extension method.

If any parameter is dynamic then compilation will fail. For example, this code will always fail: @Html.TextBox("name", ViewBag.Name). To work around this, either use ViewData["Name"] or cast the value to a specifi c type: (string) ViewBag.Name.

What is TempData?
TempData is a dictionary derived from the TempDataDictionary class and stored in a short-lived session. It is a string key and object value.

It maintains the information for the duration of an HTTP Request. This means only from one page to another. It helps to maintain data when we move from one controller to another controller or from one action to another action. In other words, when we redirect Tempdata, it helps to maintain the data between those redirects. It internally uses session variables. Temp data used during the current and subsequent request only means it is used when we are sure that the next request will be redirecting to the next view. It requires typecasting for complex data types and checks for null values to avoid errors. Generally it is used to store only one-time messages, like error messages and validation messages.

How can you define a dynamic property using viewbag in ASP.NET MVC?

Assign a key name with the syntax "ViewBag.[Key]=[ Value]" and value using the equal to operator.

For example, you need to assign a list of students to the dynamic Students property of ViewBag as in the following:List<string> students = new List<string>();countries.Add("Akhil");countries.Add("Ekta");
ViewBag.Students = students;//Students is a dynamic property associated with ViewBag.
Note: Some of the content has been taken from various books/articles.

What is ViewModel (taken from stackoverflow)?

Accepted A view model represents data that you want to have displayed on your view/page.

Let's say that you have an Employee class that represents your employee domain model and it contains the following 4 properties:public class Employee : IEntity
{
    public int Id { get; set; } // Employee's unique identifier    public string FirstName { get; set; } // Employee's first name    public string LastName { get; set; } // Employee's last name    public DateTime DateCreated { get; set; } // Date when employee was created}
View models differ from domain models in that view models only contain the data (represented by properties) that you want to use on your view. For example, let's say that you want to add a new employee record, your view model might look like this:public class CreateEmployeeViewModel{
    public string FirstName { get; set; }
    public string LastName { get; set; }}
As you can see it only contains 2 of the properties of the employee domain model. Why is this you may ask? Id might not be set from the view and it might be auto-generated by the Employee table. And DateCreated might also be set in the Stored Procedure or in the service layer of your application. So Id and DateCreated is not needed in the view model.

When loading the view/page, the create action method in your employee controller will create an instance of this view model, populate any fields if required, and then pass this view model to the view:public class EmployeeController : Controller
{
    private readonly IEmployeeService employeeService;
    public EmployeeController(IEmployeeService employeeService)
    {
        this.employeeService = employeeService;
    }
    public ActionResult Create()
    {
        CreateEmployeeViewModel viewModel = new CreateEmployeeViewModel();
        return View(viewModel);
    }
    public ActionResult Create(CreateEmployeeViewModel viewModel)
    {
        // Do what ever needs to be done before adding the employee to the database    }}
Your view might look like this (assuming you are using ASP.NET MVC3 and razor):@model MyProject.Web.ViewModels.ProductCreateViewModel <table>
<tr>
<td><b>First Name:</b></td>
<td>@Html.TextBoxFor(x => x.FirstName, new { maxlength = "50", size = "50" })@Html.ValidationMessageFor(x => x.FirstName)</td>
</tr>
<tr>
<td><b>Last Name:</b></td>
<td>@Html.TextBoxFor(x => x.LastName, new { maxlength = "50", size = "50" })@Html.ValidationMessageFor(x => x.LastName)</td>
</tr></table>
Validation would thus be done only on FirstName and LastName. Using Fluent Validation you might have validation like this:
public class CreateEmployeeViewModelValidator : AbstractValidator<CreateEmployeeViewModel>
{
    public CreateEmployeeViewModelValidator()
    {
        RuleFor(x => x.FirstName)
        .NotEmpty()
        .WithMessage("First name required")
        .Length(1, 50)
        .WithMessage("First name must not be greater than 50 characters");
        RuleFor(x => x.LastName)
        .NotEmpty()
        .WithMessage("Last name required")
        .Length(1, 50)
        .WithMessage("Last name must not be greater than 50 characters");
    }}
The key thing to remember is that the view model only represents the data that you want to use. You can imagine all the unnecessary code and validation if you have a domain model with 30 properties and you only want to update a single value. Given this scenario you would only have this one value/property in the view model and not the entire domain object.

How do you check for AJAX requests with C# in MVC.NET?

The solution is independed of the MVC.NET framework and is global across server side technologies. Most modern AJAX applications utilize XmlHTTPRequest to send async requests to the server. Such requests will have a distinct request header:

X-Requested-With = XMLHTTPREQUEST

MVC.NET provides helper functions to check for ajax requests that internally inspects the "X-Requested-With" request header to set the "IsAjax" flag.

What are Scaffold templates?

These templates use the Visual Studio T4 templating system to generate a view based on the model type selected. Scaffolding in ASP.NET MVC can generate the boilerplate code we need to create, read, update, and delete (CRUD) functionality in an application. The scaffolding templates can examine the type definition for it then generate a controller and the controller's associated views. The scaffolding knows how to name controllers, how to name views, what code needs to go to each component, and where to place all these pieces in the project for the application to work.

What are the types of Scaffolding Templates?

Empty: Creates an empty view. Only the model type is specified using the model syntax.

Create: Creates a view with a form for creating new instances of the model.
Generates a label and input field for each property of the model type.

Delete: Creates a view with a form for deleting existing instances of the model.
Displays a label and the current value for each property of the model.

Details: Creates a view that displays a label and the value for each property of the model type.

Edit: Creates a view with a form for editing existing instances of the model.
Generates a label and input field for each property of the model type.

List: Creates a view with a table of model instances. Generates a column for each property of the model type. Make sure to pass an IEnumerable<YourModelType> to this view from your action method.

The view also contains links to actions for performing the create/edit/delete operations.

Show an example of the difference in syntax in Razor and WebForm Views

Razor <span>@model.Message</span>Web Forms <span><%: model.Message %></span>

Code expressions in Razor are always HTML encoded. This Web Forms syntax also automatically HTML encodes the value.

What are Code Blocks in Views?

Unlike code expressions that are evaluated and sent to the response, blocks of code are simply sections of code that are executed. They are useful for declaring variables that we may need to use later.

Razor @{int x = 123;string y = Ëbecause.Ë;}
Web Forms
<%
int x = 123;
string y = "because.";
%>

What is the "HelperPage.IsAjax" Property?
The HelperPage.IsAjax property gets a value that indicates whether Ajax is being used during the request of the Web page.

Namespace: System.Web.WebPages
Assembly: System.Web.WebPages.dll

However, the same can be done by checking request headers directly:Request["X-Requested-With"] == "XmlHttpRequest".

Explain combining text and markup in Views using an example

This example shows what intermixing text and markup looks like using Razor as compared to Web Forms:

Razor @foreach (var item in items) {<span>Item @item.Name.</span>}
Web Forms
<% foreach (var item in items) { %>
<span>Item <%: item.Name %>.</span>
<% } %>

Explain Repository Pattern in ASP.NET MVC
In simple terms, a repository basically works as a mediator between our business logic layer and our data access layer of the application. Sometimes it would be troublesome to expose the data access mechanism directly to the business logic layer, it may result in redundant code for accessing data for similar entities or it may result in code that is hard to test or understand. To overcome these kinds of issues, and to write interface driven and test driven code to access data, we use the Repository Pattern. The repository makes queries to the data source for the data then maps the data from the data source to a business entity/domain object and finally persists the changes in the business entity to the data source. According to MSDN, a repository separates the business logic from the interactions with the underlying data source or Web Service. The separation between the data and business tiers has the following three benefits:

It centralizes the data logic or Web service access logic.

It provides a substitution point for the unit tests.

It provides a flexible architecture that can be adapted as the overall design of the application evolves.

In a Repository we write our entire business logic of CRUD operations using Entity Framework classes that will not only result in meaningful test driven code but will also reduce our controller code of accessing data.

How can you call a JavaScript function/method on the change of a Dropdown List in MVC?
Create a JavaScript method:<script type="text/javascript">    function selectedIndexChanged() {
    }</script>

Invoke the method:

<%:Html.DropDownListFor(x => x.SelectedProduct,
new SelectList(Model.Users, "Value", "Text"),
"Please Select a User", new { id = "ddlUsers",
onchange="selectedIndexChanged()" })%>

Explain Routing in MVC
A route is a URL pattern that is mapped to a handler. The handler can be a physical file, such as an .aspx file in a Web Forms application. A Routing module is responsible for mapping incoming browser requests to specific MVC controller actions.

Routing within the ASP.NET MVC framework serves the following two main purposes:

It matches incoming requests that would not otherwise match a file on the file system and maps the requests to a controller action.

It constructs outgoing URLs that correspond to controller actions.

How is a route table created in ASP.NET MVC?
When an MVC application first starts, the Application_Start() method in global.asax is called. This method calls the RegisterRoutes() method. The RegisterRoutes() method creates the route table for the MVC application.

What are Layouts in ASP.NET MVC Razor?
Layouts in Razor help maintain a consistent look and feel across multiple views within our application. Compared to Web Forms Web Forms, layouts serve the same purpose as master pages, but offer both a simpler syntax and greater flexibility.

We can use a layout to define a common template for your site (or just part of it). This template contains one or more placeholders that the other views in your application provide content for. In some ways, it's like an abstract base class for your views. For example declared at the top of view as in the following:@{Layout = "~/Views/Shared/SiteLayout.cshtml";}

What is ViewStart?
For group of views that all use the same layout, this can get a bit redundant and harder to maintain.

The "_ViewStart.cshtml" page can be used to remove this redundancy. The code within this file is executed before the code in any view placed in the same directory. This file is also recursively applied to any view within a subdirectory.

When we create a default ASP.NET MVC project, we find there is already a "_ViewStart .cshtml" file in the Views directory. It specifies a default layout as in the following:@{Layout = "~/Views/Shared/_Layout.cshtml";}
Because this code runs before any view, a view can override the Layout property and choose a different one. If a set of views shares common settings then the "_ViewStart.cshtml" file is a useful place to consolidate these common view settings. If any view needs to override any of the common settings then the view can set those values to another value.

Note: Some of the content has been taken from various books/articles.

What are HTML Helpers?

HTML helpers are methods we can invoke on the Html property of a view. We also have access to URL helpers (via the URL property) and AJAX helpers (via the Ajax property). All
these helpers have the same goal, to make views easy to author. The URL helper is also available from within the controller.

Most of the helpers, particularly the HTML helpers, output HTML markup. For example, the BeginForm helper is a helper we can use to build a robust form tag for our search
form, but without using lines and lines of code:@using (Html.BeginForm("Search", "Home", FormMethod.Get)) {<input type="text" name="q" />
<input type="submit" value="Search" />}
What is Html.ValidationSummary?The ValidationSummary helper displays an unordered list of all validation errors in the ModelState dictionary. The Boolean parameter you are using (with a value of true) is telling the helper to exclude property-level errors. In other words, you are telling the summary to display only the errors in ModelState associated with the model itself, and exclude any errors associated with a specific model property. We will be displaying property-level errors separately. Assume you have the following code somewhere in the controller action rendering the edit view:

ModelState.AddModelError("", "This is all wrong!");
ModelState.AddModelError("Title", "What a terrible name!");

The first error is a model-level error, because you didn't provide a key (or provided an empty key) to associate the error with a specific property. The second error you associated with the Title property, so in your view it will not display in the validation summary area (unless you remove the parameter to the helper method, or change the value to false). In this scenario, the helper renders the following HTML:<div class="validation-summary-errors">
<ul>
<li>This is all wrong!</li>
</ul>
</div>

Other overloads of the ValidationSummary helper enable you to provide header text and set specific HTML attributes.

NOTE: By convention, the ValidationSummary helper renders the CSS class validation-summary-errors along with any specific CSS classes you provide. The default MVC project template includes some styling to display these items in red, that you can change in "styles.css".

What are Validation Annotations?
Data annotations are attributes you can find in the "System.ComponentModel.DataAnnotations" namespace. These attributes provide server-side validation, and the framework also supports client-side validation when you use one of the attributes on a model property. You can use four attributes in the DataAnnotations namespace to cover the common validation scenarios, Required, String Length, Regular Expression and Range.

What is Html.Partial?
The Partial helper renders a partial view into a string. Typically, a partial view contains reusable markup you want to render from inside multiple different views. Partial has four overloads:public void Partial(string partialViewName);public void Partial(string partialViewName, object model);public void Partial(string partialViewName, ViewDataDictionary viewData);public void Partial(string partialViewName, object model,
ViewDataDictionary viewData);

What is Html.RenderPartial?

The RenderPartial helper is similar to Partial, but RenderPartial writes directly to the response output stream instead of returning a string. For this reason, you must place RenderPartial inside a code block instead of a code expression. To illustrate, the following two lines of code render the same output to the output stream:@{Html.RenderPartial("AlbumDisplay "); }
@Html.Partial("AlbumDisplay ")
If they are same then which one to use?

In general, you should prefer Partial to RenderPartial because Partial is more convenient (you don't need to wrap the call in a code block with curly braces). However, RenderPartial may result in better performance because it writes directly to the response stream, although it would require a lot of use (either high site traffic or repeated calls in a loop) before the difference would be noticeable.

How do you return a partial view from controller?

return PartialView(options); //options could be Model or View name

What are various ways of returning a View?

There are various ways for returning/rendering a view in MVC Razor. For example "return View()", "return RedirectToAction()", "return Redirect()" and "return RedirectToRoute()".

Conclusion
I hope we covered many of questions to brush-up. Since MVC is very vast now, I know we have missed a lot stuff too. The content in the question and answer form is also taken from few renowned books like Professional ASP.NET MVC4 from Wrox and a few of the content is taken from my MVC articles posted earlier. My future articles will provide interview questions for EntityFramework too.

MVC means ?

MVC stands for Model View Controller.
It divides an application into 3 component roles which is based on a framework methodology.
These component roles are discussed briefly as follows:

i) Models : These component roles are used to maintain the state which is persisted inside the Database.

Example: we might have a Product class that is used to represent order data from the Products table inside SQL.

ii) Views : These component roles are used to display the user interface of the application, where this UI is created off of the model data.

Example: we might create an Product “Edit” view that surfaces textboxes, dropdowns and checkboxes based on the current state of a Product object.

iii) Controllers : These component roles are used for various purposes like handling end user interaction, manipulating the model, and ultimately choosing a view to render to display UI.

Note:

In a MVC application, the views are used only for displaying the information whereas the controllers are used for handling and responding to user input and interaction.

Which assembly is used to define the MVC framework and Why ?

The MVC framework is defined through System.Web.Mvc assembly.
This is because this is the only assembly which contains classes and interfaces that support the ASP.NET Model View Controller (MVC) framework for creating Web applications.

How can we plug an ASP.NET MVC into an existing ASP.NET application ?

We can combine ASP.NET MVC into an existing ASP.NET application by following the below procedure:

First of all, you have to add a reference to the following three assemblies to your existing ASP.NET application:

i) System.Web.Routing
ii) System.Web.Abstractions
iii) System.Web.Mvc

The ASP.NET MVC folder should be created after adding these assembly references.
Add the folder Controllers, Views, and Views | Shared to your existing ASP.NET application.
And then you have to do the necessary changes in web.config file.
For this you can refer to the below link:

http://www.packtpub.com/article/mixing-aspnet-webforms-and-aspnet-mvc

What are the advantages of using asp.net mvc ?

The main advantages of using asp.net mvc are as follows:

i) One of the main advantage is that it will be easier to manage the complexity as the application is divided into model,view and controller.
ii) It gives us the full control over the behavior of an application as it does not use view state or server-based forms.
iii) It provides better support for test-driven development (TDD).
iv) You can design the application with a rich routing infrastructure as it uses a Front Controller pattern that processes Web application requests through a single controller.

Explain about Razor View Engine ?

This Razor View engine is a part of new rendering framework for ASP.NET web pages.
ASP.NET rendering engine uses opening and closing brackets to denote code (<% %>), whereas Razor allows a cleaner, implied syntax for determining where code blocks start and end.

Example:

In the classic renderer in ASP.NET:

<ul>

<% foreach (var userTicket in Model)

  { %>

    <li><%: userTicket.Value %></li>

<%  } %>

</ul>

By using Razor:

<ul>

@foreach (var userTicket in Model)

{

  <li>@userTicket.Value</li>

}

</ul>

Does the unit testing of an MVC application is possible without running controllers in an ASP.NET process ?

In an MVC application, all the features are based on interface. So, it is easy to unit test a MVC application.
And it is to note that, in MVC application there is no need of running the controllers for unit testing.

Which namespace is used for ASP.NET MVC ?

System.Web.Mvc namespace contains all the interfaces and classes which supports ASP.NET MVC framework for creating web applications.

Can we share a view across multiple controllers ?

Yes, It is possible to share a view across multiple controllers by putting a view into the shared folder.
By doing like this, you can automatically make the view available across multiple controllers.

What is the use of a controller in an MVC applicatio ?

A controller will decide what to do and what to display in the view. It works as follows:

i) A request will be received by the controller
ii) Basing on the request parameters, it will decide the requested activities
iii) Basing on the request parameters, it will delegates the tasks to be performed
iv) Then it will delegate the next view to be shown

Mention some of the return types of a controller action method ?

An action method is used to return an instance of any class which is derived from ActionResult class.
Some of the return types of a controller action method are:
i) ViewResult : It is used to return a webpage from an action method
ii) PartialViewResult : It is used to send a section of a view to be rendered inside another view.
iii) JavaScriptResult : It is used to return JavaScript code which will be executed in the user’s browser.
iv) RedirectResult : Based on a URL, It is used to redirect to another controller and action method.
v) ContentResult : It is an HTTP content type may be of text/plain. It is used to return a custom content type as a result of the action method.
vi) JsonResult : It is used to return a message which is formatted as JSON.
vii) FileResult : It is used to send binary output as the response.
viii) EmptyResult : It returns nothing as the result.

Explain about 'page lifecycle' of ASP.NET MVC ?

The page lifecycle of an ASP.NET MVC page is explained as follows:

i) App Initialisation
In this stage, the aplication starts up by running Global.asax’s Application_Start() method.
In this method, you can add Route objects to the static RouteTable.Routes collection.
If you’re implementing a custom IControllerFactory, you can set this as the active controller factory by assigning it to the System.Web.Mvc.ControllerFactory.Instance property.

ii) Routing
Routing is a stand-alone component that matches incoming requests to IHttpHandlers by URL pattern.
MvcHandler is, itself, an IHttpHandler, which acts as a kind of proxy to other IHttpHandlers configured in the Routes table.

iii) Instantiate and Execute Controller
At this stage, the active IControllerFactory supplies an IController instance.

iv) Locate and invoke controller action
At this stage, the controller invokes its relevant action method, which after further processing, calls RenderView().

v) Instantiate and render view
At this stage, the IViewFactory supplies an IView, which pushes response data to the IHttpResponse object.

Explain about NonActionAttribute ?

It is already known that all the public methods of a controller class are basically treated as action methods.
If you dont want this default behaviour, then you can change the public method with NonActionAttribute. Then, the default behaviour changes.

Explain about the formation of Router Table in ASP.NET MVC ?

The Router Table is formed by following the below procedure:

In the begining stage, when the ASP.NET application starts, the method known as Application_Start() method is called.
The Application_Start() will then calls RegisterRoutes() method.
This RegisterRoutes() method will create the Router table.

In an MVC application, what are the segments of the default route ?

There are 3 segments of the default route in an MVC application.They are:

The 1st segment is the Controller Name.
Example: search

The 2nd segment is the Action Method Name.
Example: label

The 3rd segment is the Parameter passed to the Action method.
Example: Parameter Id - MVC

What are the settings to be done for the Routing to work properly in an MVC application ?

The settings must be done in 2 places for the routing to work properly.They are:

i) Web.Config File : In the web.config file, the ASP.NET routing has to be enabled.
ii) Global.asax File : The Route table is created in the application Start event handler, of the Global.asax file.

How to avoid XSS Vulnerabilities in ASP.NET MVC ?

To avoid xss vulnerabilities, you have to use the syntax as '<%: %>' in ASP.NET MVC instead of using the syntax as '<%= %>' in .net framework 4.0.
This is because it does the HTML encoding.

Example:

<input type="text" value="<%: value%>" />

Explain the advantages of using routing in ASP.NET MVC ?

Without using Routing in an ASP.NET MVC application, the incoming browser request should be mapped to a physical file.The thing is that if the file is not there, then you will get a page not found error.
By using Routing, it will make use of URLs where there is no need of mapping to specific files in a web site.
This is because, for the URL, there is no need to map to a file, you can use URLs that are descriptive of the user's action and therefore are more easily understood by users.

What are the things that are required to specify a route ?

There are 3 things that are required to specify a route.

i) URL Pattern : You can pass the variable data to the request handler without using a query string. This is done by including placeholders in a URL pattern.
ii) Handler : This handler can be a physical file of 2 types such as a .aspx file or a controller class.
iii) Name for the Route : This name is an optional thing.

Is the route {controller}{action}/{id} a valid route definition or not and why ?

{controller}{action}/{id} is not a valid route definition.
The reason is that, it has no literal value or delimiter between the placeholders.
If there is no literal, the routing cannot determine where to seperate the value for the controller placceholder from the value for the action placeholder.

Explain about default route, {resource}.axd/{*pathInfo} ...

With the help of this default route {resource}.axd/{*pathInfo}, you can prevent requests for the web resources files such as WebResource.axd or ScriptResource.axd from being passed to a controller.

Explain the difference between adding routes, to a web application and to an mvc application ?

We use MapPageRoute() method of a RouteCollection class for adding routes to a webforms application, whereas MapRoute() method is used to add routes to an MVC application.

Is there any way to handle variable number of segments in a route definition ?

You can handle variable number of segments in a route definition by using a route with a catch-all parameter.
Example:

controller/{action}/{*parametervalues}

Here * reffers to catch-all parameter.

How do you add constraints to a route ?

There are 2 ways for adding constraints to a route. They are:
i) By using Regular Expressions and
ii) By using an object which implements IRouteConstraint interface.

Explain with examples for scenarios when routing is not applied ?

Below are the 2 scenarios where routing is not applied.

i) A Physical File is Found that Matches the URL Pattern - This default behaviour can be overriden by setting the RouteExistingFiles property of the RouteCollection object to true.
ii) Routing Is Explicitly Disabled for a URL Pattern - By using the RouteCollection.Ignore() method, you can prevent routing from handling certain requests.

Explain the usage of action filters in an MVC application ?

Action filter in an mvc application is used to perform some additional processing, such as providing extra data to the action method, inspecting the return value, or canceling execution of the action method.
Action filter is an attribute that implements the abstract FilterAttribute class.

In an MVC application, which filter executes first and which is the last ?

As there are different types of filters in an MVC application, the Authorization filter is the one which executes first and Exeption filters executes in the end.

Difference between Viewbag and Viewdata in ASP.NET MVC ?

Both are used to pass the data from controllers to views.
The difference between Viewbag and Viewdata in ASP.NET MVC is explained below:

View Data:
In this, objects are accessible using strings as keys.

Example:

In the Controller:
public ActionResult Index()
{
var softwareDevelopers = new List<string>
{
"Brendan Enrick",
"Kevin Kuebler",
"Todd Ropog"
};
ViewData["softwareDevelopers"] = softwareDevelopers;
return View();
}

In the View:
<ul>
@foreach (var developer in (List<string>)ViewData["softwareDevelopers"])
{
<li>
@developer
</li>
}
</ul>

An important note is that when we go to use out object on the view that we have to cast it since the ViewData is storing everything as object.

View Bag:
It will allow the objectto dynamically have the properties add to it.

Example:

In the Controller:
public ActionResult Index()
{
var softwareDevelopers = new List<string>
{
"Brendan Enrick",
"Kevin Kuebler",
"Todd Ropog"
};
ViewBag.softwareDevelopers = softwareDevelopers;
return View();
}

In the View:
<ul>
@foreach (var developer in ViewBag.softwareDevelopers)
{
<li>
@developer
</li>
}
</ul>

An important point to note is that there is no need to cast our object when using the ViewBag. This is because the dynamic we used lets us know the type.

What are the file extensions for razor views ?

There are two types of file extensions for razor views.
They are:

i) .cshtml : This file extension is used, when the programming language is a C#.
ii) .vbhtml : This file extension is used, when the programming language is a VB.

How can you specify comments using razor syntax ?

In razor syntax, we use the below shown symbols for specifying comments.

i) For indicating the begining of a comment, we use @* syntax.
ii) For indicating the end of a comment, we use *@ syntax.

Explain the usage of validation helpers in ASP.NET MVC ?

In ASP.NET MVC, validation helpers are used to show the validation error messages in a view.
The Html.ValidationMessage() and Html.ValidationSummary() helpers are used in the automatically generated Edit and Create views by the ASP.NET MVC.
To create a view, the following steps are to be followed:

i) In the product controller,right click on the Create() action and then select the option Add View.
ii) Now check the checkbox labeled in the Add View dialog and create a strongly-typed view.
iii) Select the product class from the View data class dropdownlist.
iv) Now, select Create from the view content dropdownlist.
v) Finally, click on the Add button.

Is it possible to create a MVC Unit Test application in Visual Studio Standard ?

No, It is not possible to create a MVC Unit Test application in Visual Studio Standard.
It is also not possible to create in Visual Studio Express.
It is possible to create only in Visual Studio Professional and Visual Studio Enterprise Versions.

What is Glimpse ?

It is an Open Source platform for gathers and presents detailed diagnostic information about the execution of your web application.It tells you exactly what's going on with each request.

We used in a similar manner to client side diagnostics and debugging tools like FireBug or Chrome Developer Tools.

It is used to reveal what is happening within your ASP.NET MVC and WebForms sites.

What are the HTML attributes that have to specify in @Html.BeginForm()?

NOTE: This is objective type question, Please click question title for correct answer.

What is the difference between Session and TempData in MVC?

NOTE: This is objective type question, Please click question title for correct answer.

How to enable JQuery intellisense support in MVC?

By default, visual studio doesn't provide Jquery intellisense support, but it can be achieved by adding vsdoc.js file to razor view.

@if(false)
{
<script src="~/script/jquery-1.7.1-vsdoc.js" type="text/javascript"></script>
}

No te : If statement prevents the rendering of script tag into the Html source code and it used only by visual studio for Jquery intellisense support.

Difference between Asp.Net MVC and Webforms?

1. Asp.net Webform follows an event-driven development model whereas Asp.net Mvc follow Model, View, Controller design pattern.

2. Asp.net Webform has server controls whereas Asp.net Mvc has Html helpers for creating UI of application.

3.Asp.net Webforms has state management techniques whereas Asp.net Mvc doesn't have automatic state management techniques.

4. Asp.net Webform has file- based Urls means file name exists in Url whereas Asp.net Mvc has route-based Url.

5. In Asp.net webform, webforms(Aspx) are tightly coupled to code-behind (Aspx.cs) whereas in Asp.net Mvc, Views and logic are kept separately.

6. Asp.net Webform has Master page for consistent look and feel whereas in Asp.net Mvc layout is for this.

7. Asp.net Webform has User Controls for code re-usability whereas in Asp.net Mvc partial view is for this.

What is partial view in Asp.Net Mvc?

A partial view is like as user control in Asp.Net web form. Partial views are reusable views like as Header and Footer. It has .csHtml extension.
Partial and RenderPartial Html method renders partial view in Mvc razor.

<div>@Html.Partial("_Comments")</div>
<div>@ { Html.RenderPartial("_Comments") } </div>

What is strongly typed view in MVC?

Strongly type view is used for rendering specific type of model object. By specifying the type of data we get intellisense for that model class. View inherits from Viewpage whereas strongly typed view inherits from Viewpage<T> where T is type of the model.

What is significance of 'using' in MVC?

@using(Html.Beginform())
{
Content Here.....
}
It ensures that an object is disposed when it goes out of scope.

How to add stylesheet in view in Asp.Net Mvc?

Add stylesheet :

<link rel="StyleSheet" href="@Href(~Content/Site.css")" type="text/css"/>

What is MvcSiteMapProvider ?

It is a tool that provides flexible menus, breadcrumb trails, and SEO features for the .NET MVC framework, similar to the ASP.NET SiteMapProvider model.

You can download it as free through NuGet package for .NET MVC 2.0/3.0/4.0

How to call an action Method on the click of a link?

NOTE: This is objective type question, Please click question title for correct answer.

What is right way to define the routes.MapRoute() method in MVC?

NOTE: This is objective type question, Please click question title for correct answer.

What is cross site request forgery (CSRF) in web application?

Cross Site Request Forgery (CSRF) is a type of attack on the web application or on the website where a malicious user can insert or update data on behalf of the logged in user of the application by giving him a link that is not of the victim website but attackers own website.

In this type of attack the victim website user doesn't know that by clicking on malicious user link he is helping him to update malicious data into his website.

This generally happen by posting data on the victim website by a hidden form and submitting in using JavaScript or jQuery automatically.

How to avoid Cross Site Request Forgery (CSRF) in ASP.NET MVC?

To avoid Cross Site Request Forgery (CSRF) in ASP.NET MVC, you need to do two things.

1. Add [ValidateAntiForgeryTocker] attribute in the Controller Action method which is executing when the form data is being submitted.

2. Add @Html.AntiForgeryTocker() element in the HTML form.

What different types of Scaffold templates are there in ASP.NET MVC?

There are 6 different types of Scaffold templates in ASP.NET MVC that is used to create a view automatically based on the Model selected.

Empty:
It creates an empty view and only model type is specified in the View page using @model

Create:
It creates a view with a form that helps to create a new record for the model. It automatically generates a label and input field for each property in the Model.

Delete :
It creates a view with the list of records from the Model collection along with Delete link to delete records.

Details:
It creates a view that displays a lable and the value of each property of the Model.

Edit
It creates a view with a form for editing existing model data. It also generates a form with label and field for each property of the Model.

List:
It creates a view with html table that lists the model from the Model collection. It generates html table column for each property of the model. In general, it accepts IEnumerable<ModelType> and iterate through each item of the Enumerable collection. It automatically renders edit, delete links for each record of the Model collection in a column and Create link on the page that target to Create action.

What is the use of ViewStart in ASP.NET MVC?

In the default template of ASP.NET MVC, we get _ViewStart.cshtml page that is used to almost similar to MasterPage in ASP.NET Web Form or like a layout template.

The code of ViewStart executes before the actual view code executes. By default, _ViewStart template is applied to all view files of this or any sub directory under this directory.

The _ViewStart.cshtml file contains following code.

@{

Layout = "~/Views/Shared/_Layout.cshtml";

}

As this code runs before any view code so we have flexibility to specify a different Layout for a particular view.

Because this code runs before any view, a view can override the Layout property and choose a different
one.

How to write dashed attributes of html (5) element using ASP.NET MVC Helper methods?

To write dashed attribute of HTML element using ASP.NET MVC Helper methods, we replace "-" with "_" in the anonymous type parameter. eg.

@using (Html.BeginForm("Create", "Home", FormMethod.Post,

new { data_validatable=true }))

returns below output

<form action="/Home/Create" method="Post" data-validatable="true" >

Notice, the data-validate attribute of the form element.

What is the use of Html.ValidationSummary helper method in ASP.NET MVC?

The Html.ValidationSummary helper method is used to display all validation errors in the ModelState dictionary, either model property level or errors associated with ModelState.

Model Property level errors are errors that are set as an attributes of the property of the Model. eg

[Required]

[StringLength(100, ErrorMessage="The Title must not be more than 100 characters long.")]

public string Title { get; set; }

In the above code, the Title field is a mandatory field and can only accept 100 characters.

The ModelState level errors are errors that are set by developer in the Controller by using below code snippet.

ModelState.AddModelError("", "There is an error!");

In this case, the error will be displayed in place of Validation summary like this

<div class="validation-summary-errors">

<ul>

<li>There is an error!</li>

</ul>

</div>

What should be the attribute for a Model property that corresponds to the Identity column of the database?

The attribute in the Model field for the Identity column of the database should be DatabaseGenerated(System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.Identity) like below

[Key]

[DatabaseGenerated(System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.Identity)] 

[Required]

public int CategoryId { get; set; }

Thanks

In case we are returning anonymous type from Controller to the views, what should be the @model in the View?

NOTE: This is objective type question, Please click question title for correct answer.

What is MVC?

MVC is a framework pattern that splits an application logic into three different roles: Model, View and Controller.

Model: Business entity on which overall application operates.MVC does not specifically mention the Data access layer as it is encapsulated by the model.

View: User interface that renders the model into a form of interaction.

Controller: Handles the request from the view and updates the model resulting in a change in model's state.

These are the three important classes(model, view and controller) required for MVC architecture.

What does Separation of concerns means?

The process of breaking a computer program into various features that overlap in functionality implies Separation of concerns.
MVC separates the content from presentation and data-processing from content.

What is ViewStart in MVC?

For group of views that all use the same layout, this can get a bit redundant and harder to maintain.
The _ViewStart.cshtml page can be used to remove this redundancy. The code within this file
is executed before the code in any view placed in the same directory. This fi le is also recursively applied to any view within a subdirectory.
When we create a default ASP.NET MVC project, we find there is already a _ViewStart
.cshtml fi le in the Views directory. It specifi es a default layout:
@{
Layout = "~/Views/Shared/_Layout.cshtml";
}
Because this code runs before any view, a view can override the Layout property and choose a different one. If a set of views shares common settings, the _ViewStart.cshtml file is a useful place to consolidate these common view settings. If any view needs to override any of the common settings, the view can set those values to another value.

How will the data gets passed between controller and views?

The controller gets the first hit and loads the model. Most of the time we would like to pass the model to the view for displaying data and so we use session variables, viewstate and so on. But the problem with using sessions or view state object is the scope. ASP.NET sessions have session scope and the view state have page scope. In MVC, we would like the data to be maintained when the hit comes to the controller and reaches the view and after that the scope of the data should expire.

That’s where the new session management technique has been introduced in the ASP.NET MVC framework, i.e., ViewData.

How to save data entered from front-end into a pdf file?

[HttpPost]
public ActionResult SaveResumeAsPdf(FormCollection fc)
{
if (Session["UserName"] != null)
{
BaseFont font = BaseFont.CreateFont(BaseFont.COURIER, BaseFont.CP1250, false);
PdfContentByte _pcb;
Document document = new Document();
try
{
PdfWriter writer = PdfWriter.GetInstance(document, new FileStream(Server.MapPath("~/Resumes/" + Session["UserName"] + ".pdf"), FileMode.Create));
document.Open();
_pcb = writer.DirectContent;
_pcb.BeginText();
_pcb.SetFontAndSize(font, 14);
int count = 30;
foreach (string item in fc.AllKeys)
{
_pcb.ShowTextAligned(PdfContentByte.ALIGN_LEFT, item, 50, 780 - count, 0);
_pcb.ShowTextAligned(PdfContentByte.ALIGN_LEFT, fc[item], 250, 780 - count, 0);
count = count + 30;
}
_pcb.EndText();
writer.Flush();
}
finally
{
document.Close();
}
}
}

How to use two models in a single class?

Whenever you want to use two models in a single view, then add the models to the view in the following way,

@using MvcSampleCFA_02032014.Models;
@model Tuple<PersonCFA, AddressCFA>

Now, you can access all the properties present in the two models.

Why do we use Repositories?

Repositories are minly used in MVC. It does not mean creating the database by itself or storing the data anywhere. It is just an approach in MVC. As we have n-tier architecture in asp.net, similarly repositories are a kind of architecture in MVC where we can create a repository class and write all the business logic in this class. We can just call this method from controller and there is no need to write any kind of business logic which makes our controller simple.

Which of the following statement is true with respect to MVC?

NOTE: This is objective type question, Please click question title for correct answer.

What is the output for the expression, string[] colors = {"green", "brown", "red", "blue"}; colors.Max(c => c.length);

NOTE: This is objective type question, Please click question title for correct answer.

How can we use css files in mvc application?

Normally, I would put most of general layout related css into content/style.css

If you use theme, then put it into content/theme/{themename}/style.css
If you create custom html control, i would try to create another css file for control and put it under content/control.css
In most of time, jquery is used in the asp.net MVC, so it make sense to put it's css in Script/jquery/{pluginName}/xxx.css
There could be more, but that's what's in my head now.

Splitting the css into multiple files is a good thing from a maintenace point of view. It makes it easier to work with and apply changes. However, multiple files can have an impact on application performance as the browser has to download each file individually. You can haev the best of both worlds though.

The technique that is recommended is to bundle all your html files for deployment so that it is served as 1 single file. The nice thing about this approach is that it lets you develop with multiple files, giving you ease of use. But get on the fly css file combination so that your browser only has to download one file.

What is used for Code-Reusability in Asp.Net Mvc ?

Business Layer in Asp.Net Mvc is also known as ?

Display Layer in Asp.Net Mvc is also known as ?

Input Control in Asp.Net Mvc is also known as ?

In Asp.Net Mvc, the property that provides access to the route data structure for current request is ?

Who introduced first MVC to the world ?

In Asp.Net MVC 'ActionResults', which Result is used to return a string literally ?

In Asp.Net MVC 'ActionResults', which Result is used to return the contents of a file ?

In Asp.Net MVC 'ActionResults', which Result is used to return a script to execute ?

In Asp.Net MVC 'ActionResults', which Result is used to return the data in JSON format ?

In Asp.Net MVC 'ActionResults', which Result is used to Redirect the client to a new Url ?

In Asp.Net MVC 'ActionResults', which Result is used to return an HTTP 403 status ?

In Asp.Net MVC 'ActionResults', which Result is used to Redirect client to another action or another controller's action ?

In Asp.Net MVC 'ActionResults', the Result responsible for the View Engine's response ?

In Asp.Net MVC 'ActionResults', the Result used to get no response ?

In Asp.Net MVC, the Action Filter used to cache the output of a controller is ?

In Asp.Net MVC, the Html helper used to create a 'form' tag is ?

In Asp.Net MVC, the Html helper used to render the Checkbox in Razor is ?

In Asp.Net MVC, the Html helper used to render the RadioButton control in Razor is ?

In Asp.Net MVC, the Html helper used to render a DropDown list in Razor is ?

In Asp.Net MVC, the Html helper used to create the 'password' type input is ?

In Asp.Net MVC, the Html helper used to create an input with 'hidden' type is ?

In Asp.Net MVC, the Html helper used to render a simple Textbox in Razor view is ?

In Asp.Net MVC, the Html helper used to render a large text space in Razor view is ?

In Asp.Net MVC, Html helper used for creating a Listbox in Razor view is ?

In Asp.Net MVC, the Html helper used to reuse the partial view's code in Razor is ?

In Asp.Net MVC, the Html helper that allows to setup a sub request inside of the primary Mvc request is ?

In Asp.Net MVC, the Entity framework approach that can import the database and generate all the classes you need to query and update the database ?

In Asp.Net MVC, the Entity Framework approach used to draw a conceptual model for your application and the genere in your database schema ?

In Asp.Net MVC, the Entity framework approach to write the c# classes and use those class definitions to create the database ?

In Asp.Net MVC, the Html helper used for creating a label in Razor view is ?

In Asp.Net MVC, the Attribute used to prevent the Cross-Site Request Forgery is ?

What is the difference between Url.RouteUrl and Url.HttpRouteUrl?

Url.RouteUrl is used to generate a fully qualified URL for specified route values by using a route name configured in App_Start/RouteConfig.cs file.

@Url.RouteUrl("MyCustomRoute", new { action = "New", id = 12, Name = "Sheo" })

gives output as /CustomController/New/12?Name=Sheo

Url.HttpRouteUrl is also used to generate fully qualified URL for the specified route values but for Web API Routes. Internally this method add an "httproute" entry to routeValues. GetVirtualPath method of the Web Api route classes return null unless we include "httproute" in the values.

@Url.HttpRouteUrl("MyCustomRoute", new { action = "New", id = 12, Name = "Sheo" })</p>

gives output as /CustomController/New/12?Name=Sheo&httproute=True.

Notice httproute query-string at the end.

In MVC is mandatory to be Map route {controller}/{action}/{id} In This format only..??

Its not mandatory to be URL string must be in controller/action/params format.

If User defined in his RouteConfig file like {controller}/{action}/{id} Query string will be controller/action/id.

if user defined in his RouteConfig file like {action}/{controller}/{id} Query string will be
Action/controlleer/id.

What is the difference between Html.EditorFor and Html.TextBoxFor in ASP.NET MVC?

Html.EditorFor

@Html.EditorFor(model => model.LastName)

This HTML helper method is very dynamic in nature. Based on which type of data is passed to this method, the output changes.

For example,
1. if model property type is of string type, it renders a textbox
2. if the property type is boolean type it renders a checkbox.
3. if the property type is of integer type, it render input type="number" textbox.

In order to control the output of the Html.EditorFor we can use EditorTemplates for different data types.

Html.TextBoxFor

@Html.TextBoxFor(model => model.LastName)

This HTML helper method only renders a TextBox as output irrespective of whatever data type the model property is of.

Explain about ViewData VS ViewBag Vs TempData in MVC

2014-07-14T00:19:00.001-07:00

Introduction

ViewData and ViewBag are used for the same purpose to transfer data from controller to view. Both life lies only in current request. ViewData is nothing but dictionary of object and it is accessible by string as key. ViewData is property of controller that exposes an instance of the ViewDataDictionary class. ViewBag is very similar to ViewData. ViewBag is a dynamic property (dynamic keyword which is introduced in .net framework 4.0). ViewBag is able to set and get value dynamically and able to add any number of additional fields without converts it to strongly typed. ViewBag is just a wrapper around the ViewData.

ViewData Example

//Controller Code

public ActionResult Index()

{

List<string> Student = new List<string>();

Student.Add("Jignesh");

Student.Add("Tejas");

Student.Add("Rakesh");

ViewData["Student"] = Student;

return View();

}

//page code

<ul>

<% foreach (var student in ViewData["Student"] as List<string>)

{ %>

<% } %>

</ul>

ViewBag Example

//Controller Code

public ActionResult Index()

{

List<string> Student = new List<string>();

Student.Add("Jignesh");

Student.Add("Tejas");

Student.Add("Rakesh");

ViewBag.Student = Student;

return View();

}

//page code

<ul>

<% foreach (var student in ViewBag.Student)

{ %>

<% } %>

</ul>

TempData is a dictionary which is derived from TempDataDictionary class. TempData is stored data just like live session for short time. TempData Keep data for the time of HTTP Request it mean that it hold data between two consecutive requests. TempData help us to transfer data between controllers or between actions. TempData internally use Session variables. Note that TempData is only work during the current and subsequent request. It is generally used to store one time message. With the help of TempData.Keep() method we can keep value in TempData object after request completion.

TempData Example

//Controller Code

public ActionResult Index()

{

List<string> Student = new List<string>();

Student.Add("Jignesh");

Student.Add("Tejas");

Student.Add("Rakesh");

TempData["Student"] = Student;

return View();

}

//page code

<ul>

<% foreach (var student in TempData["Student"] as List<string>)

{ %>

<% } %>

</ul>

ViewData VS ViewBag VS TempData

ViewData	ViewBag	TempData
It is Key-Value Dictionary collection	It is a type object	It is Key-Value Dictionary collection
ViewData is a dictionary object and it is property of ControllerBase class	ViewBag is Dynamic property of ControllerBase class.	TempData is a dictionary object and it is property of controllerBase class.
ViewData is Faster than ViewBag	ViewBag is slower than ViewData	NA
ViewData is introduced in MVC 1.0 and available in MVC 1.0 and above	ViewBag is introduced in MVC 3.0 and available in MVC 3.0 and above	TempData is also introduced in MVC1.0 and available in MVC 1.0 and above.
ViewData is also work with .net framework 3.5 and above	ViewBag is only work with .net framework 4.0 and above	TempData is also work with .net framework 3.5 and above
Type Conversion code is required while enumerating	In depth, ViewBag is used dynamic, so there is no need to type conversion while enumerating.	Type Conversion code is required while enumerating
It value become null if redirection is occurred.	Same as ViewData	TempData is used to pass data between two consecutive requests.
It lies only during the current request.	Same as ViewData	TempData is only work during the current and subsequent request

Conclusion

We have three options ViewData, ViewBag and TeampData for passing data from controller to view and in next request. ViewData and ViewBag are almost similar and it helps us to transfer the data from controller to view whereas TempData is also work during the current and subsequent request.

Explain about MVC Breafly

2014-06-25T02:40:00.001-07:00

Disclaimer

Reading these MVC interview questions does not mean you will go and clear MVC interviews. The purpose of this article is to quickly brush up your MVC knowledge before you go for MVC interviews. This article does not teach MVC, it’s a last minute revision sheet before going for MVC interviews.
If you want to learn MVC from scratch, start by reading Learn MVC ( Model view controller) step by step 7 days or you can also start with my step by step MVC (Model View Controller) video series from YouTube.

Need help to improve this article

I have tried my level best to cover what questions i have faced in MVC interviews. But i feel the below questions are not enough and in real MVC interview's much more is asked. If you can share your question in the comment below. I would love to incorporate them in this article so that others are benefited.
If your question is great and i like it i will ship you a free copy of my .NET interview question book only in India ( sorry i am not so rich for outside countries).

What is MVC (Model View Controller)?

MVC is an architectural pattern which separates the representation and user interaction. It’s divided into three broader sections, Model, View, and Controller. Below is how each one of them handles the task.

The View is responsible for the look and feel.
Model represents the real world object and provides data to the View.
The Controller is responsible for taking the end user request and loading the appropriate Model and View.

Figure: MVC (Model view controller)

Explain MVC application life cycle?

There are six broader events which occur in MVC application life cycle below diagrams summarize it.

Any web application has two main execution steps first understanding the request and depending on the type of the request sending out appropriate response. MVC application life cycle is not different it has two main phases first creating the request object and second sending our response to the browser.
Creating the request object: -The request object creation has four major steps. Below is the detail explanation of the same.
Step 1 Fill route: - MVC requests are mapped to route tables which in turn specify which controller and action to be invoked. So if the request is the first request the first thing is to fill the route table with routes collection. This filling of route table happens in the global.asax file.
Step 2 Fetch route: - Depending on the URL sent “UrlRoutingModule” searches the route table to create “RouteData” object which has the details of which controller and action to invoke.
Step 3 Request context created: - The “RouteData” object is used to create the “RequestContext” object.
Step 4 Controller instance created: - This request object is sent to “MvcHandler” instance to create the controller class instance. Once the controller class object is created it calls the “Execute” method of the controller class.
Creating Response object: - This phase has two steps executing the action and finally sending the response as a result to the view.

Is MVC suitable for both Windows and Web applications?

The MVC architecture is suited for a web application than Windows. For Window applications, MVP, i.e., “Model View Presenter” is more applicable. If you are using WPF and Silverlight, MVVM is more suitable due to bindings.

What are the benefits of using MVC?

There are two big benefits of MVC:

Separation of concerns is achieved as we are moving the code-behind to a separate class file. By moving the binding code to a separate class file we can reuse the code to a great extent.
Automated UI testing is possible because now the behind code (UI interaction code) has moved to a simple .NET class. This gives us opportunity to write unit tests and automate manual testing.

Is MVC different from a three layered architecture?

MVC is an evolution of a three layered traditional architecture. Many components of the three layered architecture are part of MVC. So below is how the mapping goes:

Functionality	Three layered / tiered architecture	Model view controller architecture
Look and Feel	User interface	View
UI logic	User interface	Controller
Business logic /validations	Middle layer	Model
Request is first sent to	User interface	Controller
Accessing data	Data access layer	Data Access Layer

Figure: Three layered architecture

What is the latest version of MVC?

When this note was written, four versions were released of MVC: MVC 1 , MVC 2, MVC 3, and MVC 4. So the latest is MVC 4.

What is the difference between each version of MVC?

Below is a detailed table of differences. But during an interview it’s difficult to talk about all of them due to time limitation. So I have highlighted the important differences that you can run through before the interviewer.

MVC 2	MVC 3	MVC 4
Client-side validation Templated Helpers Areas Asynchronous Controllers `Html.ValidationSummary` Helper Method `DefaultValueAttribute` in Action-Method Parameters binding Binary data with Model Binders DataAnnotations Attributes Model-Validator Providers New `RequireHttpsAttribute` Action Filter Templated Helpers Display Model-Level Errors	Razor Readymade project templates HTML 5 enabled templates Support for Multiple View Engines, JavaScript, and AJAX Model Validation Improvements	ASP.NET Web API Refreshed and modernized default project templates. New mobile project template. Many new features to support mobile apps Enhanced support for asynchronous methods

What are HTML helpers in MVC?

HTML helpers help you to render HTML controls in the view. For instance if you want to display a HTML textbox on the view , below is the HTML helper code.

<%= Html.TextBox("LastName") %>

For checkbox below is the HTML helper code. In this way we have HTML helper methods for every HTML control that exists.

<%= Html.CheckBox("Married") %>

What is the difference between “HTML.TextBox” vs “HTML.TextBoxFor”?

Both of them provide the same HTML output, “HTML.TextBoxFor” is strongly typed while “HTML.TextBox” isn’t. Below is a simple HTML code which just creates a simple textbox with “CustomerCode” as name.

Html.TextBox("CustomerCode")

Below is “Html.TextBoxFor” code which creates HTML textbox using the property name ‘CustomerCode” from object “m”.

Html.TextBoxFor(m => m.CustomerCode)

In the same way we have for other HTML controls like for checkbox we have “Html.CheckBox” and “Html.CheckBoxFor”.

What is routing in MVC?

Routing helps you to define a URL structure and map the URL with the controller.
For instance let’s say we want that when a user types “http://localhost/View/ViewCustomer/”, it goes to the “Customer” Controller and invokes the DisplayCustomer action. This is defined by adding an entry in to the routes collection using the maproute function. Below is the underlined code which shows how the URL structure and mapping with controller and action is defined.

routes.MapRoute(
               "View", // Route name
               "View/ViewCustomer/{id}", // URL with parameters
               new { controller = "Customer", action = "DisplayCustomer", 
id = UrlParameter.Optional }); // Parameter defaults

Where is the route mapping code written?

The route mapping code is written in the “global.asax” file.

Can we map multiple URL’s to the same action?

Yes, you can, you just need to make two entries with different key names and specify the same controller and action.

How can we navigate from one view to another using a hyperlink?

By using the ActionLink method as shown in the below code. The below code will create a simple URL which helps to navigate to the “Home” controller and invoke the GotoHome action.

<%= Html.ActionLink("Home","Gotohome") %>

How can we restrict MVC actions to be invoked only by GET or POST?

We can decorate the MVC action with the HttpGet or HttpPost attribute to restrict the type of HTTP calls. For instance you can see in the below code snippet the DisplayCustomer action can only be invoked by HttpGet. If we try to make HTTP POST on DisplayCustomer, it will throw an error.

[HttpGet]
public ViewResult DisplayCustomer(int id)
{
    Customer objCustomer = Customers[id];
    return View("DisplayCustomer",objCustomer);
}

How can we maintain sessions in MVC?

Sessions can be maintained in MVC by three ways: tempdata, viewdata, and viewbag.

What is the difference between tempdata, viewdata, and viewbag?

Figure: Difference between tempdata, viewdata, and viewbag

Temp data - Helps to maintain data when you move from one controller to another controller or from one action to another action. In other words when you redirect, tempdata helps to maintain data between those redirects. It internally uses session variables.
View data - Helps to maintain data when you move from controller to view.
View Bag - It’s a dynamic wrapper around view data. When you use Viewbag type, casting is not required. It uses the dynamic keyword internally.

Figure: dynamic keyword

Session variables - By using session variables we can maintain data from any entity to any entity.
Hidden fields and HTML controls - Helps to maintain data from UI to controller only. So you can send data from HTML controls or hidden fields to the controller using POST or GET HTTP methods.

Below is a summary table which shows the different mechanisms for persistence.

Maintains data between	ViewData/ViewBag	TempData	Hidden fields	Session
Controller to Controller	No	Yes	No	Yes
Controller to View	Yes	No	No	Yes
View to Controller	No	No	Yes	Yes

What are partial views in MVC?

Partial view is a reusable view (like a user control) which can be embedded inside other view. For example let’s say all your pages of your site have a standard structure with left menu, header, and footer as shown in the image below.

Figure: Partial views in MVC

For every page you would like to reuse the left menu, header, and footer controls. So you can go and create partial views for each of these items and then you call that partial view in the main view.

How did you create a partial view and consume it?

When you add a view to your project you need to check the “Create partial view” check box.

Figure: Create partial view

Once the partial view is created you can then call the partial view in the main view using the Html.RenderPartial method as shown in the below code snippet:

<body>
<div>
<% Html.RenderPartial("MyView"); %>
</div>
</body>

How can we do validations in MVC?

One of the easiest ways of doing validation in MVC is by using data annotations. Data annotations are nothing but attributes which can be applied on model properties. For example, in the below code snippet we have a simple Customer class with a property customercode.
This CustomerCode property is tagged with a Required data annotation attribute. In other words if this model is not provided customer code, it will not accept it.

public class Customer
{
    [Required(ErrorMessage="Customer code is required")]
    public string CustomerCode
    {
        set;
        get;
    } 
}

In order to display the validation error message we need to use the ValidateMessageFor method which belongs to the Html helper class.

<% using (Html.BeginForm("PostCustomer", "Home", FormMethod.Post))
{ %>
<%=Html.TextBoxFor(m => m.CustomerCode)%>
<%=Html.ValidationMessageFor(m => m.CustomerCode)%>
<input type="submit" value="Submit customer data" />
<%}%>

Later in the controller we can check if the model is proper or not by using the ModelState.IsValid property and accordingly we can take actions.

public ActionResult PostCustomer(Customer obj)
{
    if (ModelState.IsValid)
    {
        obj.Save();
        return View("Thanks");
    }
    else
    {
        return View("Customer");
    }
}

Below is a simple view of how the error message is displayed on the view.

Figure: Validations in MVC

Can we display all errors in one go?

Yes, we can; use the ValidationSummary method from the Html helper class.

<%= Html.ValidationSummary() %>

What are the other data annotation attributes for validation in MVC?
If you want to check string length, you can use StringLength.

[StringLength(160)]
public string FirstName { get; set; }

In case you want to use a regular expression, you can use the RegularExpression attribute.

[RegularExpression(@"[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,4}")]public string Email { get; set; }

If you want to check whether the numbers are in range, you can use the Range attribute.

[Range(10,25)]public int Age { get; set; }

Sometimes you would like to compare the value of one field with another field, we can use the Compare attribute.

public string Password { get; set; }[Compare("Password")]public string ConfirmPass { get; set; }

In case you want to get a particular error message , you can use the Errors collection.

var ErrMessage = ModelState["Email"].Errors[0].ErrorMessage;

If you have created the model object yourself you can explicitly call TryUpdateModel in your controller to check if the object is valid or not.

TryUpdateModel(NewCustomer);

In case you want add errors in the controller you can use the AddModelError function.

ModelState.AddModelError("FirstName", "This is my server-side error.");

How can we enable data annotation validation on client side?

It’s a two-step process: first reference the necessary jQuery files.

<script src="<%= Url.Content("~/Scripts/jquery-1.5.1.js") %>" type="text/javascript"></script>
<script src="<%= Url.Content("~/Scripts/jquery.validate.js") %>" type="text/javascript"></script>
<script src="<%= Url.Content("~/Scripts/jquery.validate.unobtrusive.js") %>" type="text/javascript"></script>

The second step is to call the EnableClientValidation method.

<% Html.EnableClientValidation(); %>

What is Razor in MVC?

It’s a light weight view engine. Till MVC we had only one view type, i.e., ASPX. Razor was introduced in MVC 3.

Why Razor when we already have ASPX?

Razor is clean, lightweight, and syntaxes are easy as compared to ASPX. For example, in ASPX to display simple time, we need to write:

<%=DateTime.Now%>

In Razor, it’s just one line of code:

@DateTime.Now

So which is a better fit, Razor or ASPX?

As per Microsoft, Razor is more preferred because it’s light weight and has simple syntaxes.

How can you do authentication and authorization in MVC?

You can use Windows or Forms authentication for MVC.

How to implement Windows authentication for MVC?

For Windows authentication you need to modify the web.config file and set the authentication mode to Windows.

<authentication mode="Windows"/>
<authorization>
<deny users="?"/>
</authorization>

Then in the controller or on the action, you can use the Authorize attribute which specifies which users have access to these controllers and actions. Below is the code snippet for that. Now only the users specified in the controller and action can access it.

[Authorize(Users= @"WIN-3LI600MWLQN\Administrator")]
public class StartController : Controller
{
    //
    // GET: /Start/
    [Authorize(Users = @"WIN-3LI600MWLQN\Administrator")]
    public ActionResult Index()
    {
        return View("MyView");
    }
}

How do you implement Forms authentication in MVC?

Forms authentication is implemented the same way as in ASP.NET. The first step is to set the authentication mode equal to Forms. The loginUrl points to a controller here rather than a page.

<authentication mode="Forms">
<forms loginUrl="~/Home/Login"  timeout="2880"/>
</authentication>

We also need to create a controller where we will check if the user is proper or not. If the user is proper we will set the cookie value.

public ActionResult Login()
{
    if ((Request.Form["txtUserName"] == "Shiv") && 
          (Request.Form["txtPassword"] == "Shiv@123"))
    {
        FormsAuthentication.SetAuthCookie("Shiv",true);
        return View("About");
    }
    else
    {
        return View("Index");
    }
}

All the other actions need to be attributed with the Authorize attribute so that any unauthorized user making a call to these controllers will be redirected to the controller (in this case the controller is “Login”) which will do the authentication.

[Authorize]
PublicActionResult Default()
{
return View();
}
[Authorize]
publicActionResult About()
{
return View();
}

How to implement AJAX in MVC?

You can implement AJAX in two ways in MVC:

AJAX libraries
jQuery

Below is a simple sample of how to implement AJAX by using the “AJAX” helper library. In the below code you can see we have a simple form which is created by using the Ajax.BeginForm syntax. This form calls a controller action called getCustomer. So now the submit action click will be an asynchronous AJAX call.

<script language="javascript">
function OnSuccess(data1) 
{
// Do something here
}
</script>
<div>
<%
        var AjaxOpt = new AjaxOptions{OnSuccess="OnSuccess"};        
    %>
<% using (Ajax.BeginForm("getCustomer","MyAjax",AjaxOpt)) { %>
<input id="txtCustomerCode" type="text" /><br />
<input id="txtCustomerName" type="text" /><br />
<input id="Submit2" type="submit" value="submit"/></div>
<%} %>

In case you want to make AJAX calls on hyperlink clicks, you can use the Ajax.ActionLink function as shown in the below code.

Figure: Implement AJAX in MVC

So if you want to create an AJAX asynchronous hyperlink by name GetDate which calls the GetDate function in the controller, below is the code for that. Once the controller responds, this data is displayed in the HTML DIV tag named DateDiv.

<span id="DateDiv" />
<%: 
Ajax.ActionLink("Get Date","GetDate",
new AjaxOptions {UpdateTargetId = "DateDiv" })
%>

Below is the controller code. You can see how the GetDate function has a pause of 10 seconds.

public class Default1Controller : Controller
{
   public string GetDate()
   {
       Thread.Sleep(10000);
       return DateTime.Now.ToString();
   }
}

The second way of making an AJAX call in MVC is by using jQuery. In the below code you can see we are making an AJAX POST call to a URL /MyAjax/getCustomer. This is done by using $.post. All this logic is put into a function called GetData and you can make a call to the GetData function on a button or a hyperlink click event as you want.

function GetData() 
{
    var url = "/MyAjax/getCustomer";
    $.post(url, function (data) 
    {
        $("#txtCustomerCode").val(data.CustomerCode);
        $("#txtCustomerName").val(data.CustomerName);
    }
    )
}

What kind of events can be tracked in AJAX?

Figure: Tracked in AJAX

What is the difference between ActionResult and ViewResult?

ActionResult is an abstract class while ViewResult derives from the ActionResult class. ActionResult has several derived classes like ViewResult, JsonResult, FileStreamResult, and so on.
ActionResult can be used to exploit polymorphism and dynamism. So if you are returning different types of views dynamically, ActionResult is the best thing. For example in the below code snippet, you can see we have a simple action called DynamicView. Depending on the flag (IsHtmlView) it will either return a ViewResult or JsonResult.

public ActionResult DynamicView()
{
   if (IsHtmlView)
     return View(); // returns simple ViewResult
   else
     return Json(); // returns JsonResult view
}

What are the different types of results in MVC?

Note: It’s difficult to remember all the 12 types. But some important ones you can remember for the interview are ActionResult, ViewResult, and JsonResult. Below is a detailed list for your interest:
There 12 kinds of results in MVC, at the top is the ActionResult class which is a base class that can have 11 subtypes as listed below:

ViewResult - Renders a specified view to the response stream
PartialViewResult - Renders a specified partial view to the response stream
EmptyResult - An empty response is returned
RedirectResult - Performs an HTTP redirection to a specified URL
RedirectToRouteResult - Performs an HTTP redirection to a URL that is determined by the routing engine, based on given route data
JsonResult - Serializes a given ViewData object to JSON format
JavaScriptResult - Returns a piece of JavaScript code that can be executed on the client
ContentResult - Writes content to the response stream without requiring a view
FileContentResult - Returns a file to the client
FileStreamResult - Returns a file to the client, which is provided by a Stream
FilePathResult - Returns a file to the client

What are ActionFilters in MVC?

ActionFilters help you to perform logic while an MVC action is executing or after an MVC action has executed.

Figure: ActionFilters in MVC

Action filters are useful in the following scenarios:

Implement post-processing logic before the action happens.
Cancel a current execution.
Inspect the returned value.
Provide extra data to the action.

You can create action filters by two ways:

Inline action filter.
Creating an ActionFilter attribute.

To create an inline action attribute we need to implement the IActionFilter interface. The IActionFilter interface has two methods: OnActionExecuted and OnActionExecuting. We can implement pre-processing logic or cancellation logic in these methods.

public class Default1Controller : Controller , IActionFilter
{
    public ActionResult Index(Customer obj)
    {
        return View(obj);
    }
    void IActionFilter.OnActionExecuted(ActionExecutedContext filterContext)
    {
        Trace.WriteLine("Action Executed");
    }
    void IActionFilter.OnActionExecuting(ActionExecutingContext filterContext)
    {
        Trace.WriteLine("Action is executing");
    }
}

The problem with the inline action attribute is that it cannot be reused across controllers. So we can convert the inline action filter to an action filter attribute. To create an action filter attribute we need to inherit from ActionFilterAttribute and implement the IActionFilter interface as shown in the below code.

public class MyActionAttribute : ActionFilterAttribute , IActionFilter
{
    void IActionFilter.OnActionExecuted(ActionExecutedContext filterContext)
    {
        Trace.WriteLine("Action Executed");
    }
    void IActionFilter.OnActionExecuting(ActionExecutingContext filterContext)
    {
      Trace.WriteLine("Action executing");
    }
}

Later we can decorate the controllers on which we want the action attribute to execute. You can see in the below code I have decorated the Default1Controller with the MyActionAttribute class which was created in the previous code.

[MyActionAttribute]
public class Default1Controller : Controller 
{
    public ActionResult Index(Customer obj)
    {
        return View(obj);
    }
}

Can we create our custom view engine using MVC?

Yes, we can create our own custom view engine in MVC. To create our own custom view engine we need to follow three steps:
Let’ say we want to create a custom view engine where in the user can type a command like “<DateTime>” and it should display the current date and time.
Step 1: We need to create a class which implements the IView interface. In this class we should write the logic of how the view will be rendered in the render function. Below is a simple code snippet for that.

public class MyCustomView : IView
{
    private string _FolderPath; // Define where  our views are stored
    public string FolderPath
    {
        get { return _FolderPath; }
        set { _FolderPath = value; }
    }

    public void Render(ViewContext viewContext, System.IO.TextWriter writer)
    {
       // Parsing logic <dateTime>
        // read the view file
        string strFileData = File.ReadAllText(_FolderPath);
        // we need to and replace <datetime> datetime.now value
        string strFinal = strFileData.Replace("<DateTime>", DateTime.Now.ToString());
        // this replaced data has to sent for display
        writer.Write(strFinal); 
    }
}

Step 2: We need to create a class which inherits from VirtualPathProviderViewEngine and in this class we need to provide the folder path and the extension of the view name. For instance, for Razor the extension is “cshtml”; for aspx, the view extension is “.aspx”, so in the same way for our custom view, we need to provide an extension. Below is how the code looks like. You can see the ViewLocationFormats is set to the Views folder and the extension is “.myview”.

public class MyViewEngineProvider : VirtualPathProviderViewEngine
{
    // We will create the object of Mycustome view
    public MyViewEngineProvider() // constructor
    {
        // Define the location of the View file
        this.ViewLocationFormats = new string[] { "~/Views/{1}/{0}.myview", 
          "~/Views/Shared/{0}.myview" }; //location and extension of our views
    }
    protected override IView CreateView(
      ControllerContext controllerContext, string viewPath, string masterPath)
    {
        var physicalpath = controllerContext.HttpContext.Server.MapPath(viewPath);
        MyCustomView obj = new MyCustomView(); // Custom view engine class
        obj.FolderPath = physicalpath; // set the path where the views will be stored
        return obj; // returned this view paresing
        // logic so that it can be registered in the view engine collection
    }
    protected override IView CreatePartialView(ControllerContext controllerContext, string partialPath)
    {
        var physicalpath = controllerContext.HttpContext.Server.MapPath(partialPath);
        MyCustomView obj = new MyCustomView(); // Custom view engine class
        obj.FolderPath = physicalpath; // set the path where the views will be stored
        return obj;
        // returned this view paresing logic
        // so that it can be registered in the view engine collection
    }
}

Step 3: We need to register the view in the custom view collection. The best place to register the custom view engine in the ViewEngines collection is the global.asax file. Below is the code snippet for that.

protected void Application_Start()
{
    // Step3 :-  register this object in the view engine collection
    ViewEngines.Engines.Add(new MyViewEngineProvider());
    &hellip;..
}

Below is a simple output of the custom view written using the commands defined at the top.

Figure: Custom view engine using MVC

If you invoke this view, you should see the following output:

How to send result back in JSON format in MVC

In MVC, we have the JsonResult class by which we can return back data in JSON format. Below is a simple sample code which returns back a Customer object in JSON format using JsonResult.

public JsonResult getCustomer()
{
    Customer obj = new Customer();
    obj.CustomerCode = "1001";
    obj.CustomerName = "Shiv";
    return Json(obj,JsonRequestBehavior.AllowGet);
}

Below is the JSON output of the above code if you invoke the action via the browser.

What is WebAPI?

HTTP is the most used protocol. For the past many years, browser was the most preferred client by which we consumed data exposed over HTTP. But as years passed by, client variety started spreading out. We had demand to consume data on HTTP from clients like mobile, JavaScript, Windows applications, etc.
For satisfying the broad range of clients REST was the proposed approach. You can read more about REST from the WCF chapter.
WebAPI is the technology by which you can expose data over HTTP following REST principles.

But WCF SOAP also does the same thing, so how does WebAPI differ?

	SOAP	WEB API
Size	Heavy weight because of complicated WSDL structure.	Light weight, only the necessary information is transferred.
Protocol	Independent of protocols.	Only for HTTP protocol
Formats	To parse SOAP message, the client needs to understand WSDL format. Writing custom code for parsing WSDL is a heavy duty task. If your client is smart enough to create proxy objects like how we have in .NET (add reference) then SOAP is easier to consume and call.	Output of WebAPI are simple string messages, JSON, simple XML format, etc. So writing parsing logic for that is very easy.
Principles	SOAP follows WS-* specification.	WebAPI follows REST principles. (Please refer to REST in WCF chapter.)

With WCF you can implement REST, so why WebAPI?

WCF was brought into implement SOA, the intention was never to implement REST. WebAPI is built from scratch and the only goal is to create HTTP services using REST. Due to the one point focus for creating REST service, WebAPI is more preferred.

How to implement WebAPI in MVC

Below are the steps to implement WebAPI:
Step 1: Create the project using the WebAPI template.

Figure: Implement WebAPI in MVC

Step 2: Once you have created the project you will notice that the controller now inherits from ApiController and you can now implement POST, GET, PUT, and DELETE methods of the HTTP protocol.

public class ValuesController : ApiController
{
    // GET api/values
    public IEnumerable<string> Get()
    {
        return new string[] { "value1", "value2" };
    }
    // GET api/values/5
    public string Get(int id)
    {
        return "value";
    }
    // POST api/values
    public void Post([FromBody]string value)
    {
    }
    // PUT api/values/5
    public void Put(int id, [FromBody]string value)
    {
    }
    // DELETE api/values/5
    public void Delete(int id)
    {
    }
}

Step 3: If you make an HTTP GET call you should get the below results:

Figure: HTTP

How can we detect that an MVC controller is called by POST or GET?

To detect if the call on the controller is a POST action or a GET action we can use the Request.HttpMethod property as shown in the below code snippet.

public ActionResult SomeAction()
{
    if (Request.HttpMethod == "POST")
    {
        return View("SomePage");
    }
    else
    {
        return View("SomeOtherPage");
    }
}

What is bundling and minification in MVC?

Bundling and minification helps us improve request load times of a page thus increasing performance.

How does bundling increase performance?

Web projects always need CSS and script files. Bundling helps us combine multiple JavaScript and CSS files in to a single entity thus minimizing multiple requests in to a single request.
For example consider the below web request to a page . This page consumes two JavaScript files Javascript1.js and Javascript2.js. So when this is page is requested it makes three request calls:

One for the Index page.
Two requests for the other two JavaScript files: Javascript1.js and Javascript2.js.

The below scenario can become worse if we have a lot of JavaScript files resulting in multiple requests, thus decreasing performance. If we can somehow combine all the JS files into a single bundle and request them as a single unit that would result in increased performance (see the next figure which has a single request).

So how do we implement bundling in MVC?

Open BundleConfig.cs from the App_Start folder.

In BundleConfig.cs, add the JS files you want bundle into a single entity in to the bundles collection. In the below code we are combining all the javascript JS files which exist in the Scripts folder as a single unit in to the bundle collection.

bundles.Add(new ScriptBundle("~/Scripts/MyScripts").Include(
"~/Scripts/*.js"));

Below is how your BundleConfig.cs file will look like:

public  class BundleConfig
{
    public static void RegisterBundles(BundleCollection bundles)
    {
        bundles.Add(new ScriptBundle("~/Scripts/MyScripts").Include(
           "~/Scripts/*.js"));
        BundleTable.EnableOptimizations = true;
    }
}

Once you have combined your scripts into one single unit we then to include all the JS files into the view using the below code. The below code needs to be put in the ASPX or Razor view.

<%= Scripts.Render("~/Scripts/MyScripts")  %>

If you now see your page requests you would see that script request is combined into one request.

How can you test bundling in debug mode?

If you are in a debug mode you need to set EnableOptimizations to true in the bundleconfig.cs file or else you will not see the bundling effect in the page requests.

BundleTable.EnableOptimizations = true;

Explain minification and how to implement it

Minification reduces the size of script and CSS files by removing blank spaces , comments etc. For example below is a simple javascript code with comments.

// This is test
var x = 0;
x = x + 1;
x = x * 2;

After implementing minification the JavaScript code looks like below. You can see how whitespaces and comments are removed to minimize file size, thus increasing performance.

var x=0;x=x+1;x=x*2;

How do we implement minification?

When you implement bundling, minification is implemented by itself. In other words the steps to implement bundling and minification are the same.

Explain Areas in MVC?

Areas help you to group functionalities in to independent modules thus making your project more organized. For example in the below MVC project we have four controller classes and as time passes by if more controller classes are added it will be difficult to manage. In bigger projects you will end up with 100’s of controller classes making life hell for maintenance.

If we can group controller classes in to logical section like “Invoicing” and “Accounting” that would make life easier and that’s what “Area” are meant to.

You can add an area by right clicking on the MVC solution and clicking on “Area” menu as shown in the below figure.

In the below image we have two “Areas” created “Account” and “Invoicing” and in that I have put the respective controllers. You can see how the project is looking more organized as compared to the previous state.

Explain the concept of View Model in MVC?

A view model is a simple class which represents data to be displayed on the view.
For example below is a simple customermodel object with “CustomerName” and “Amount” property.

Collapse | Copy Code

CustomerViewModel obj = new CustomerViewModel();
obj.Customer.CustomerName = "Shiv";
obj.Customer.Amount = 1000;

But when this “Customer” model object is displayed on the MVC view it looks something as shown in the below figure. It has “CustomerName” , “Amount” plus “Customer Buying Level” fields on the view / screen. “Customer buying Level” is a color indicationwhich indicates how aggressive the customer is buying.
“Customer buying level” color depends on the value of the “Amount property. If the amount is greater than 2000 then color is red , if amount is greater than 1500 then color is orange or else the color is yellow.
In other words “Customer buying level” is an extra property which is calculated on the basis of amount.

So the Customer viewmodel class has three properties

“TxtCustomerName” textbox takes data from “CustomerName” property as it is.
“TxtAmount” textbox takes data from “Amount” property of model as it is.
“CustomerBuyingLevelColor” displays color value depending on the “Amount “ value.

Customer Model	Customer ViewModel
CustomerName	TxtCustomerName
Amount	TxtAmount
	CustomerBuyingLevelColor

What kind of logic view model class will have?

As the name says view model this class has the gel code or connection code which connects the view and the model.
So the view model class can have following kind of logics:-

Color transformation logic: - For example you have a “Grade” property in model and you would like your UI to display “red” color for high level grade, “yellow” color for low level grade and “green” color of ok grade.
Data format transformation logic :-Your model has a property “Status” with “Married” and “Unmarried” value. In the UI you would like to display it as a checkbox which is checked if “married” and unchecked if “unmarried”.
Aggregation logic: -You have two differentCustomer and Address model classes and you have view which displays both “Customer” and “Address” data on one go.
Structure downsizing: - You have “Customer” model with “customerCode” and “CustomerName” and you want to display just “CustomerName”. So you can create a wrapper around model and expose the necessary properties. How can we use two ( multiple) models with a single view? Let us first try to understand what the interviewer is asking. When we bind a model with a view we use the model dropdown as shown in the below figure. In the below figure we can only select one model.

But what if we want to bind “Customer” as well as “Order” class to the view.
For that we need to create a view model which aggregates both the classes as shown in the below code. And then bind that view model with the view.

Collapse | Copy Code
```
public class CustOrderVM
{
public  Customer cust = new Customer();
public Order Ord = new Order();
}
```
In the view we can refer both the model using the view model as shown in the below code.

Collapse | Copy Code
```
<%= model.cust.Name %>
<%= model.Ord.Number %>
```
Explain the need of display mode in MVC?
Display mode displays views depending on the device the user has logged in with. So we can create different views for different devices anddisplay mode will handle the rest.
For example we can create a view “Home.aspx” which will render for the desktop computers and Home.Mobile.aspx for mobile devices. Now when an end user sends a request to the MVC application, display mode checks the “user agent” headers and renders the appropriate view to the device accordingly.

Explain MVC model binders?
Model binder maps HTML form elements to the model. It acts like a bridge between HTML UI and MVC model. Many times HTML UI names are different than the model property names. So in the binder we can write the mapping logic between the UI and the model.

Real Time Scenario Based Interview Questions

2014-06-24T03:21:00.003-07:00

Hai Friends,
As we know that getting more experience and then going for the interview requires more knowledge and if we see, it requires more practical knowledge.
So in the continuation, I am trying to post few questions of OOPS which are scenario based and will be helpful when you are going for the interviews with 3+ years experience. These questions will definitely make you to think something more which you were thinking before about the answer of a particular question. With the hope that these questions and answers will be helpful to you, I am posting them and will try to update and include more in the future.
These questions are scenario based questions in .Net technologies which will help to prepare for the interviews. Few questions are related to OOP’s concepts, and then few on Garbage Collector and memory related. So you can prepare them accordingly. These questions will be useful for those who are having the 3+ years experience and looking out for the opportunities in good companies.

1. How the Encapsulation is different from Abstraction? I think both are used to hide the unnecessary details? Then how they are different?
Ans.

Yes, Both Encapsulation and Abstraction do the same thing but with few differences.

Encapsulation mainly encapsulates the object and so hides the details as well as it binds the data.

So Encapsulation = Hiding + Binding the data

How it hides the data? Real-time Example?

Take the example of n-Tier application where we have an additional layer called Business Objects. This layer

contains all the entities with their properties. Take an entity name: Employee. This Employee will have the

class name "EmployeeBO.cs" and contains the public properties like EmpId, EmpName, Sal ets

EmployeeBO.cs

So this is the presentation of one property in the Business object class. Now wherever we want this attribute,

We just need to create the object of this class and set/get the value of EmpId as:

// set the EmpId

EmployeeBo objEmployeeBO = new EmployeeBO();

objEmployeeBO.EmpId = 101;

// get the EmpId

int empId = objEmployeeBO.EmpID;

Now the question is where its setting or getting the value?

EmpId is the public property in the EmployeeBO class and contain no value. Only _empId contains the value

which is private and so it is not accessible.

So binding of the data happens to the EmpId through _empID and hiding happends through _empId which is

private. The Data is accessed through the Public property while the actual data is in private variable. So

binding + hiding using Encapsulation.

Abstraction is to ignore the unnecessary details and get the required details. So it also hides the unnecessary details. How?

Abstract class is the special type of class which can contain the abstract and concrete members. If we define

The member (Method/Property) as abstract, it must be overrides to the child class. We are not bothering here About the non-abstract or concrete members. Which is an unnecessary detail? If we ad an additional concrete Member in the abstract class, we need not to do anything in the child class. But if we add the abstract members, we must have to override it. So abstract doesn't care about the concrete members which are unnecessary for it and so it hides those details.

2. What do you mean by early binding and late binding in the object bindings? Which is good? Please give me a scenario where you have used the early binding and late binding concepts in your application?

Ans.In .Net, the early binding and last binding concepts comes under the polymorphism. As we know that there are 2 types of polymorphism-

1. Compile Time polymorphism

2. Run time polymorphism

The Compile Time polymorphism also called as the Overloading where we have the same method name with different behaviors. By implementing the multiple prototype of the same method, we can achieve the behavior of the Overloading.

Also this behavior is valid only for a single class. It means we should have all the overloaded methods in the same class.

e.g.

The Run time polymorphism also named as the Overriding. This concept works in between classes or multiple classes or parent child classes where the child class has to get the behavior of the base class by inheriting the base class.

In this concept we generally have an abstract or virtual method in the base class and we override that method in the child class by using the override method.

e.g.

So now we know the Compile Time polymorphism and Run Time polymorphism. The compile time polymorphism uses the concept of early binding and Run time polymorphism uses it as the late binding.

In early binding, the runtime (CLR) gets the behavior in the compilation of the program. It means that the method behavior will get compiled before in the early binding.

In Late binding, like Overriding, the behavior of the class and methods gets by the CLR when creating the object means at runtime. So, in the late binding the behavior of the class members identified by the CLR at runtime.

Now come to the next part of the question-which is good?

One can’t say about the answer of this question, there are the scenarios where the early binding is good. When you have lot of objects and in that case, the early binding behavior performs well. While the late binding will be good when we have less objects. Let’s say you want the dropdown list to be loaded when you click on it and not while the loading of the page. So in some scenario, it will be good if we have while load and it will not be good when you click.

So it’s all depends on how you have implemented and the form structure.

3. In garbage collection, how the object generations come in the picture? How many generations an object can have? Please tell me the process of disposing the objects based on the generations? Can an object move from one generation to another? If yes then why? What’s the need to have different generations as we are going to dispose the objects which are marked by the Garbage collector?
Ans.

Let’s start with what is Garbage collection first and then we will come to our main question of the post. As we know that all the objects created using the new operator gets fits in to the Heap memory. So whenever a new object gets created, it tries to fit in the heap memory. Now let’s say the heap memory is full and there is no place to keep another newly created object.

In that case the Garbage collector installed, which is the background process, runs through CLR and take the unused objects memory. It mainly cleanup the heap memory and the newobjects get placed in to it.

Now the question comes that for which objects it reclaims for the memory? How the object generations come in the picture?

It depends on the objects generations. The CLR finds out the objects which are no longer used by the application since longer time and then the Garbage collection reclaim their memory.

How many generations an object can have? Please tell me the process of disposing the objects based on the generations?

Actually there are 3 generations exists for the objects which are written under the .Net framework library. When a new object gets created, by default it moves to the generation 0.

Can an object move from one generation to another?

Now when the generation 0 objects gets occupied with the memory and garbage collector gets called by the run-time. It checks the objects which are no longer used by the application and mark them for deletion. After deleting or reclaim the memory, the older objects moved to next generation i.e. Generation 1. Now the next time the CLR will check for the Generation 1 object too and if it finds that in generation 1 if the objects are not used since longer time, it will mark them for release and move the remaining objects to generation 2.

In generation the objects which are under the main method, exists as they gets removed either at the end of the program or when both the generation 0 and generation 1 objects are using.

What’s the need to have different generations as we are going to dispose the objects which are marked by the Garbage collector?

With the different generation, it improves the performance of the application as the Garbage collector need not to check for each of the objects in the memory. It first checks for the generation 0 objects and reclaim the memory. If still needs then goes to the generation 1 and then 2.

4. What is object graph in garbage collector? Is this the graph physically exists? Or how this graph gets created?
Ans. When the Garbage Collector gets called by the CLR to DE-allocate the memory in the heap, the Garbage Collector start finding the references of all the reachable objects which are currently in use. So it find the objects which are used by the processes and for rest of objects which are un-reachable or the Garbage collector is not able to find the references for them, it marks them for deletion.

Here the Garbage collector makes an Object graph which keeps track of all the objects which are marked for deletion. After the deleting the references for those objects, the heap memory gets compacted and a new root becomes available to use by the new created object.

Is this the graph physically exists? Or how this graph gets created?

No, this object graph creates virtually by the Garbage Collector to keep all the objects and to make them for deletion. This is the Garbage Collector responsibility to create this object graph and gets the references of each reachable object which are used by the application

5.     Can we suppress the Garbage collector? If yes, then why do we need to suppress it as it is used to reclaim the unused memory and which improve s the performance of our application?
Ans. Yes, We can suppress the Garbage Collector. There is the Static method in GC class called as SupressFinalize.
  GC.SuppressFinalize(objectName);
This Static method takes a parameter for the object. So we can pass it to suppress the claiming memory for this object.
Now the question comes "why do we need to suppress it as it is used to reclaim the unused memory",
So, whenever we are using dispose method for class object,which is capable of disposing the object and in that case we don't need to use this method to again reclaim the memory.
e.g.
  public class DemoClass : IDisposable

   public void Dispose()

    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }

As we have seen above,the DemoClass is inherited by IDisposable interface and which have the Dispose method to implement.
Hence after implementation of Dispose() method, we need not to reclaim the memory using the Garbage collector and so we can use the SuppressFinalize() for the current class object.

6. We already have the Finalize method which reclaims the memory using the Garbage collector. This is automatic process then why do we have the Dispose () method? Is this method different from Finalize ()? What is the interface from which the Dispose () method inherited?
Ans. Yes, We have the Finalize() method which is used to reclaim the memory for the unused objects. The Finalize() method is sufficient to release the memory from heap for the un-referenced object but it is only for the managed objects. So Finalize() method can reclaim the managed objects memory from the heap which are not used since longer time.
Then what about the objects which are unmanaged? The objects which are out of .Net CLR? The objects where the CLR can't be used to manage? Dispose() method is used for all those objects which do not comes under CLR or under the Managed heap. Dispose() method can be overrides and can be written to reclaim the object of those classes. Dispose() method is implemented by using the IDisposable interface.
e.g.

public class TestClass : IDisposable
{

  public void Dispose()

 {
    Dispose(true);
 }
}

7. Can we call the Finalize() method to be executed explicitly when we want that particular object memory to be reclaim by the Garbage Collector? If yes, then where do we need to write the code? If no then why?

8. Can we inherit child class from 2 base classes? If yes then how? If not then why? What is this scenario called as in OOPs? How to implement this kind of scenario where we need to inherit the methods from more than one base class?

9. How the Virtual methods are different from General methods? Can we have a method in the base class and then in the child class can we write the same method? If not? Why? What is the error we will get if we write the same method in the child class with the same name as the parent class method name?

10. Why do we need abstract class or abstract members? Can’t we simply write the general methods and fulfill our requirements? Can we get any advantage by implantation of abstract members? As per the abstract class scenario, let’s say we have an abstract method called Show () in the abstract base class. Now if I am inheriting this base class to a child class, we need to override this abstract method to the child class. And then we will call this method by creating instance of child class.Now if we only have the method in the child class and then create the instance and call the same method? Then why abstract class method? Is that method doing anything here?

11. How abstract class and interfaces are different? Can’t we create an abstract class by having all the members as abstract members and wherever required inherit and implement its members? Then why interface? I think interface is also doing the same thing? Then how they are different?

12. Can we have abstract properties in Interface? If yes, then how to write the syntax for the abstract property which is having the return type string?

13. Can we write static methods inside a non-static class? Is it possible to call a non-static method inside the static method? If yes then how?

14. Shadowing is the special type of overriding? How? Please explain?

15. When we inherit a class which is having the private members. Are the private members also gets inherited? If yes? Why cant’ we get them by the class object? If no then why?

16.  What is the Difference between Coupling and Cohesion? If the components are more cohesive the software is good? Or vice versa?

17. See the below code snippet and think about the output.

18.  What is the Difference between HTTP enabled WCF Service and Web Services? I think if we restrict the WCF service just for the HTTP communication, both WCF and Web Service will have the same behavior. Then why still people prefer to have the WCF service rather than the Web Service. What all the things which can be achieved through HTTP enabled WCF service and cant be just from Web Service.

19.  What is the Difference between SOAP enabled Services and ReST Services? Which one is preferred and why?

........................................................................................................

1. Why we used Inheritance. What is the benefit of this.
Ans. Inheritance is a way to inherit the base class members to the child class so that we can save lot of memory.
let's say, if you are already having some properties defined in the base class and then if you are inheriting this base class to the child class, the extra memory need not to be wasted to declare the base class members again. While inheriting, automatically they will be inherited.
e.g.

class Mybase
{
int i, j;
float z;
}
class MyChild: Mybase
{
// no need to declare again the above variables
// as they will be automatically inherited.
}

As we need not to declare the variables again in the child class, so we have saved here 4 + 4 + 8 = 16 bytes of memory for the child class.
Main usage of inheritance is 'Re-usability'. No need to declare variables, methods again.. If u want, then use them from base class. It reduce your code from complexity.
2. Why C# does not support Multiple Inheritance.
Ans. Multiple Inheritance is the situation in which when there are 2 base class and a single child class is trying to inherit the members from both of them then there is the confusion that which base class member should be inherited?
e.g.

class MyClass1
{
public void Show()
{
// something
}
}
class MyClass2
{
public void Show()
{
// something else
}
}
class MyChildClass: MyClass1, MyClass2
{
// not possible
}

Due to this, the architecture of .Net or the framework doesn't support such situation and will throw the compile time error.
In C++, it is possible because there both the methods in the different base classes will have the different memory location and object will be accessed through the memory location. But in Java or .Net the object accessed through the class members objects.
It is quite difficult to implement multiple inheritance in C#. But we can do this through Interfaces.
3. Why we used virtual keyword.
Ans. If we want to override the members of the base class, we can make them as virtual. The virtual members have the capability to override them in the child class. If they are not overridden, the base class implementation will be executed.
It is not the mandatory to override the virtual class members.
e.g.

class MybaseClass
{
public virtual void Show()
{
Console.WriteLine("hey..I am in base class");
}
}

class MyChild: MyBaseClass
{
public override void Show()
{
Console.WriteLine("hey..I am in child class");
}
}

The preference will be given to child class always.

public static void Main(string[] args)
{
MyChild objChild = new MyChild();
objChild.Show(); // child class method will be called.
}

If a base class method needs to be overridden, it is defined using the keyword virtual (otherwise the sealed keyword is used to prevent overriding).
4. If my base class does not have virtual keyword but both class have same method , parameter and return type. then what will happen. base class method will be called or only child class method will called.
Ans. By default the preference will be given to child class. The child class method will be called always. If you want to call the base class method, then you need to use the base keyword likebase.MethodName()
5. What are events and actions in c#.
Ans. Events are the objects which are binded with the particular action. Whenever an action happens, an event fires. Like button click event.The action is click and event is Button_Click which is attached with the event handler to do the particular action and get the result.
6. What is user define function in SQL or What are the user define function available in SQL.
Ans. There are 2 types of functions in SQL Server-
1. Inline functions
2. Tabular functions
Inline functions gives the result as a single value while the tabular functions return the multiple values like a table.
Both of these types of function can be created as user defined. Means we can create our own function which can be inline or Tabular by using their syntax.

Create function
return int[/Table]
as
Select FirstName+ LastName from Emp where EmpId = 101;
Create Function
return Table
as
Select * from Emp;

7. If we have one Master Page , one aspx page and one ascx page then which one will called 1st while page_load event and which one called 1st while page_Unload event.
Ans. If the content page contains the user controls then below will be the calling route-
Master Page Load event --> Content Page Load event --> User control page Load event
While unloading:
Content page Unload --> user control unload --> Master page unload event
8. What is Indexers and please give the description with example.
Ans. Indexer are the objects which doesn't need to be initialized and we can use them as it is for the storing and retrieving the data in to pages.
Indexer is represented as []. So we can use them in Session, Application types of objects when keeping the state management data.
e.g.

ViewState["UserName"] = txtUserName.Text;
Session["UserName"] = txtUserName.Text;
Application["UserName"] = txtUserName.Text;

To retrieve these data, we can simply type cast them as :

lblUserName.Text = ViewState["UserName"] as string;
lblUserName.Text = Session["UserName"] as string;
lblUserName.Text = Application["UserName"] as string;

Here you can see that there is no need to create object of the indexers. Directly we can retrieve the data.
9. What are indexes in Database. How many types of Indexes in SQL Server
Ans. Indexing is used to increase the performance of a query, instead of performing the entire table scan the query uses the index to execute the query.
There are five types of indexes in the SQL Server database:
1. Clustered Index
2. Non-Clustered Index
3. KeySet Index
4. Default Insex
5. XML Index
One thing here to remember that the Indexes retrieves the data by using the Binary tree formats.
1. Clustered Index:- Those indexes which can be maximum 1 per table and they will be the key to retrieve the data. the clustered indexes retrieves the data in the B-Tree format and improve the performance of the retrieval from the table.
e.g. There are 1000 records in the table and the user want to retrieve the 234th record. Without index, the table scan will compare the record in whole table to get the matched record. So for the 1000 records, it will match for 999 times. If it found the records in the beginning, then also it will search the whole table.
Whn using the index, the below process will occur for the searching of 234th record:
1. It will take the 234th record as the root and compare the table by partitioning it in to two parts.1-500 and 501-1000
2. then it compares with the left and right and then it will found that 234 is less than 500 so leave the right part.
3. Now comparing will happen for the 1-250 and then 250-500. For this, it will check that 234 will come in the 1-250 range so leave the other part.
4. Now the comparison will be 1-125 and 126-250...and so on..
So if you calculate the total comparison it will be hardly 8-9. So we have reduces almost 990 comparison to improve the performance.
In Clustered index, the actual data exists at the leaf root of the B-tree and it search the data directly.
2. Non-Clustered Index:- it searches the data in B+ tree format where the leaf node contains the memory location of the data. Once it gets the actual memory location, by using the reference it retrieve the actual data.There can be more than one Non-Clustered indexes per table.
There can be 249 non-clustered index(in SQL Server 2005) and 999 non-clustered index (SQL Server 2008).
3. KeySet Indexes:- Only keys are stored and not the actual data. the search will happens based on the key. Once the key found, it searches the complete data for the key. So its faster than all the indexes.
4. Default Index:- When the primary is added to the table, by default the index gets created called as Default Index.
5. XML index:- When the index is created on the XML column, the index is called as the XML index. This type of index gets introduces since SQL Server 2005 version. XML type column is supported since SQL Server 2005.
10.Why we use Interface.
Ans.Interface is a way to use the global functionality throughout the application. If your application require many unrelated object types to provide certain functionality then you go for interfaces.
It defines a contract between the application and the object.
Let's suppose we want to Show the data or Print the data in many pages of the application, we can create a Interface which will contain the Abstract method and in the page where we want, we can implement it as per our requirements.
e.g.

interface inf
{
void Print(); // abstract method
}
internal class MyClass: inf
{
public void Print()
{
// functionality to print to PDF document
}
}
internal class MyTest: inf
{
public void Print()
{
// functionality to print to tiff document
}
}
internal Class MyTest: inf
{
public void Print()
{
// functionality to print to .jpg format
}
}

We can see here we have separate classes and the implementation of the Print method is different without making any changes in our interface.
So if we want to implement something global, we can use the Interface, for local or limited to class, we can use the abstract class.
11.Why we use Method Overloading
Ans. To reduce the memory and the good readability, we use the Overloading. This is the concept where we can have the same method name for similar work with different behavior.
Let's say we want to get the Database connection based on the provider name to connect with different databases, we can use the overloaded methods like:

public string GetConnectionString()
{
// return default connection string
}
public string GetConnectionString(string provider)
{
// return connection string based on provider name
}

12. Why we use Method Overriding
Ans. Method overriding is the concept where we can use the same method in parent as well as in child class to reduce the memory and use the similar behavior. If we don't want to change the behavior, we need not to override it. So to make the changes in the behavior, we use the overriding.
13. What is the difference between Abstraction and Encapsulation.
Ans. Encapsulation is the biding and hiding of the data while Abstraction is to get the essential information from the raw data.
e.g. Encapsulation

class Test
{
private string _name;
public string Name
{
set _name= value;
return _name;
}
}

Here the _name is the private which is not accessible so hiding the data. All the data will be binded to the private variable as per the statement

set _name= value;

This property will be accessed by the public member called Name.
So Binding and hiding means encapsulation.
Abstraction is done by using the abstract class where we can have abstract and non abstract members.
When ever we are having the abstract members, we need to implement it/override them in the child class to use them.

class MyBaseClass
{
public abstract void Displaye();
}
class MyChildClass: MyBaseClass
{
public override void Display()
{
// do something
}
}

Here the essential things is the abstract method which must be overridden. If we add any number of non-abstract method, the child class wont care. So Getting the essential information is Abstraction.
14. In which case we can use Abstract class in our project.
Ans. Abstract class is always used when we have the limited scope or the objects are of similar types.
e.g. Lets suppose we want to get the area of few objects. This is not the global where we need to do.
So we can create the abstract method to calculate the area and then according to shape, we can override them. So here the scope is limited and will not be used throughout the application.
Hence we can use the abstract class.
15. What is the difference between Array List and Ilist.
Ans. IList is an interface for the implementing the List collection.
As the List is the generic so we can use it to restrict the type of the list e g.

List objList = new List();

It means, the List object is restricted to the int. We can't insert here any type of data in to list. Only the int is permitted.
ArrayList is the collection where we can insert any type of data as:

ArrayList objArrayList = new ArrayList();
objArrayList.Add("Hello");
objArrayList.Add(1);
objArrayList.Add("Sure");

The ArrayList will not check the type in the compilation of the program.
16. What is difference between internal class and sealed class.
Ans. The internal class object can be used with-in the assembly and not outside of the assembly. These classes can be inherited.
Sealed classes are those classes which doesn't need anything from outside. These are full classes.
These classes can't be extended.
17.

public void show(int x , string y)
public void show(string x , int y)

Is this method overloading or what is it?
Ans. no, this is not the method overloading because, their signatures are not same
Signature= Method Name + Argument types

Show(int, string)
Show(string, int)

Both signatures are different. So not overloading methods.

public void show(int x , string y)
public void show(string x , int y)

Is this method overloading or what is it?
Ans: it is method overloading. As per method overloading the method should differ
- type of parameters
- Order of parameters
- number of parameters
18. What is the difference between Remoting and web service.
Ans. Remoting is the concept of calling the remote interfaces like communication with the heterogeneous applications but both should be developed using the same .Net language.
For the client and server communication, we use the Remoting.
Remoting is the platform dependent so both the client and server must be built in .Net Technology and both the systems should use the CLR.
Web-service is small logic which runs on the internet. It is used for the heterogeneous applications and consume the service in any application. It is platform independent so no need to have the CLR or .net framework to be installed on the machines. C++ web service can be consumes in .Net application.
19. Can we use viewstate in MVC.
Ans. No, ViewState cannot be used in MVC. There is no concept of ViewState in the MVC as it is not required. The MVC views are not having anything server side code so the view only be rendered and not loaded.
To pass the data from one page to another, we can use the ViewBag.

The reason we use MVC is to separate business logic from your view or UI and the site should be easily testable.
ViewState mixes your business logic with your UI, while MVC separates the Business Logic from the UI.

Asp.Net MVC Interview Questions

2014-06-24T03:20:00.001-07:00

Hey Friends,

Now a days we can see lot of companies asking about the ASP.net MVC related questions in their interviews. So i thought of to keep few questions which are related to the ASP.Net MVC and they will be helpful for all of them who are going for the interviews or preparing for the ASP.Net MVC.

Here I kept many questions which are related to all the versions of ASP.Net MVC to keep in mind that interviewer can ask the questions from various aspects.

1. What is MVC?

Ans. MVC (Model View Controller) is one of the Software Architectural pattern which is built on 3 layers. So it is the pattern which basically talks about the separation of concern for a project. Here the 3 parts are having their own roles like:

a. Model - It is used as the Data Container or it can also have the business rules, functions, logic's etc.

b. View - It is mainly the UI (User Interface) part which is the main application built using the Web technologies like ASP.Net etc. It consists of the User Interface Design, representation of the information for the end users etc.

c. Controller - It is the mediator between the View and Model and used to control the requests and responses floating through the views and Model. The command, Actions, Events are the part of Controller in MVC. All the communication is done via Controller so we can say that Controller is the heart of MVC.

2. What is ASP.Net MVC?

Ans. ASP.Net MVC is the Microsoft product based on the core MVC pattern. The Microsoft has taken the core concept of MVC and Designed the ASP.Net MVC structure for the Visual Studio which helps the developers to get the automated structure and on it, they can built the applications.

ASP.Net MVC provides the structure with the separation of concerns where each part of ASP.Net MVC application is separate and has no link among them. Apart from the separation of concerns, the Microsoft has provided the way to communicate between the separate components by using the other additional logic and libraries. These libraries supports in the connection, communication between the components, databases and other external components as well with small effort.

3. How ASP.net MVC is different than MVC?

Ans. ASP.Net MVC is the inherited form of Core MVC where Microsoft has designed their MVC patterns based on the original core MVC concept. The Microsoft also provided the new MVC structure (ASP.Net MVC) which has the inbuilt capabilities of communication with their components, connection with the database etc. The ASP.Net MVC has the good support for creating mobile application. We can create the Mobile applications in ASP.Net MVC using the predefined template.

4. What are the new features of ASP.Net MVC 2?

Ans. There are few major changes happened in the version MVC2. The Microsoft has more concentrated on the HTML Helpers, Validations support, Async controllers etc.Below are the few point which distinguishes the ASP.Net MVC 2 different than the previous versions:
a. New HTML Helpers with Strongly Typed
b. Model based validations- This is very useful feature where the validation is done in the Model and will be used throughout the application.
c. Automatic scaffolding feature also got introduces with this version.
d. Asynchronous controller support which enables the multiple tasks to run simultaneously.
e. Html.RenderAction introduced to render the section/part of the page.

5. Explain MVC Architecture?
Ans.

6. What are the new features of ASP.Net MVC 3?

7. What are the new features of ASP.Net MVC 4?

8. Explain ASP.Net MVC application life cycle?

9. Advantages of MVC Framework?

10. What do you mean by Separation of Concerns?

11. Where do we see Separation of Concerns in MVC?

12. What is Razor View Engine in ASP.Net MVC 3?

13. Explain the advantages of using routing in ASP.NET MVC?

14. What are the things that are required to specify a route ? Which is a better fit, Razor or ASPX?

15. How can you do authentication and authorization in ASP.Net MVC?

16. How to implement Windows authentication for ASP.Net MVC?

17. How do you implement Forms authentication in ASP.Net MVC? Mention some of the return types of a controller action method

18. Is ASP.Net MVC suitable for both Windows and web applications?

19. What are the benefits of using ASP.Net MVC?

20. Is MVC different from a three layered architecture?

21. What is the latest version of ASP.Net MVC?

22. What is the difference between each version of ASP.Net MVC?

23. What are HTML helpers in MVC?

24. What is the difference between "HTML.TextBox" vs "HTML.TextBoxFor" in ASP.Net MVC?

25. What is routing in MVC?

26. Where is the route mapping code written?

27. Can we map multiple URLs to the same action?

28. How can we navigate from one view to other view using a hyperlink?

29. How can we restrict MVC actions to be invoked only by GET or POST?

30. How can we maintain sessions in MVC?

31. What is the difference between tempdata, viewdata, and viewbag?

32. What are partial views in ASP.Net MVC?

33. How do you create a partial view and consume it in ASP.Net MVC 4?

34. How can we do validations in ASP.Net MVC?

35. Can we display all errors in one go? or Validation summery in ASP.Net MVC.

36. How can we enable data annotation validation on the client side?

37. What is Razor in MVC?

38. Why Razor when we already have ASPX?

39. How to implement AJAX in MVC

40. What kind of events can be tracked in AJAX?

41. What is the difference between ActionResult and ViewResult?

42. What are the different types of results in MVC?

43. What are ActionFilters in MVC?

44. Can we create our own custom view engine using MVC?

45. How to send result back in JSON format in MVC

46. What is WebAPI?

47. But WCF SOAP also does the same thing, so how does WebAPI differ? With WCF you can implement REST, so why WebAPI?

48. How can we detect that a MVC controller is called by POST or GET?

49. What is Bundling and Minification in MVC?

50. How does bundling increase performance?

51. How do we implement bundling in MVC?

52. How can you test bundling in debug mode?

53. Explain minification and how to implement it. How do we implement minification?

54. Explain Areas in MVC?

55. Explain the concept of View Model in MVC?

56. What kind of logic view model class will have?

57. How can we use two ( multiple) models with a single view?

Dotnet Interview Questions For 3+ Years of Experiance

2014-06-24T03:18:00.001-07:00

Hai Friends,
Below I am posting the questions and answers for the short questions for 3-6 years guys. These questions will be helpful for those who are preparing for the interview or attending the interviews. This will be helpful for the last minute preparation in quickest way.
If anyone has better answer, please reply to this post as that will be useful for all of us.

CLR and C#

1. Types of Authentication and Authorization in IIS.
A. Types of Authentication: Anonymous Authentication, Windows Authentication, Digest Authentication
Types of Authorization:- Anonymous

2. Types of Authentication and Authorization in ASP.Net.
A. Types of Authentication: Windows Authentication, Forms Authentication
Types of Authorization:- File Authorization and URL Authorization

3. ASP.Net Life cycle.
A. The request starts with the client and processed through IIS. In IIS, there are 2 utilities- INetInfo.exe and ASPNet_ISAPI.dll the InetInfo.exe checks for the syntax and semantics of the request and then the request goes to the ASPNet_ISAPI.dll which is the filter to filter the .aspx files. Here the URL request split in to 2 parts- virtual directory and webpage. Now worker process which is nothing but the application factory basically contains all the virtual directories and checks for the current virtual directory. If this is first request, then there will be no Virtual directory available. Now the worker process (W3wp.exe) creates a memory area called as AppDomain to check for the current page. As AppDomain is the Page Handler factory so it contains all the processes pages. If this is the new page then it will not find here. The request further move to the HttpPipeline where the actual execution of the page happened by using the ProcessRequest method and creates the events of the page. After creation of event and execution of all the event, the HTML page gets back to the user.

4. ASP.Net Page Life Cycle.
A. There are few events which gets generated during the page execution like: Page_BeginRequest, Page_Init, Page_Load, Page_Prerender, Page_Render, Page_Unload etc
For the details of the page life cycle, you can follow the previous question.

5. What are types: Value Type and Reference Type?
A. Value type holds data directly, Value type stored in the stack memory, we can get the direct value of the value types. Value type data type can’t be null.
Reference types: This type doesn’t hold the data directly. They hold the address on which the actual data present. They stored in heap memory, Can have default values.
We can make and work with null reference type.

6. Boxing and Unboxing: Terminology, Advantages and Disadvantages.
A. Converting the value type data type in to the Reference type is called as Boxing. Converting the Reference type data type and keep its value to stack is called as the reference type.
byte b= 45;
Object o = b.Tostring();
The Advantage of boxing and unboxing is that we can convert the type of the object in to another type. The disadvantage is that it requires lot of memory and CPU cycles to convert from one type to another type.
Object o=10;
Int i= Convert.ToInt32(o.ToString());

7. What is Type Safety?
A. TypeSafe is a way through which the application or framework that the memory will not be leaked to outside environment. E.g. C# is the type safe language where you must have to assign any object before using it. In VB.Net it will take the default value. So C# is the type safe language while VB.Net is not.

8. What is Strong Name?
A. Strong Name (SN) is used to make the dll as the unique as:
SN -k fileName.dll
Now it will have the unique name. This assembly when placed in the GAC, it will treat as the unique with its version number and other details. 2 assemblies with the same name can exist in the GAC but both will have different version. The CLR takes the latest version assembly while running the application.

9. What are Extensions, modules and handlers?
A. HttpModule and HttpHandler are the utilities which are used in the HttpPipeline under the ASP.Net page life cycle. When the request received to HttpPipeline, the HttpModule checks for the Authentication of the request and then it route the request to the respective handler. After that HttpHandler takes that request and process it. After Processing the request again the HttpModule takes the response and send it back to the worker process and finally to the user.

10. What is worker process?
A. Worker process (w3wp.exe) is an executable which is also called as the Application Factory. This is used for the execution of the request and handling of the request for the current web page.

11. CLR and DLR?
A. CLR (Common Language Runtime) is the utility in the .Net framework to run the application. It is the run-time engine which actually executes the application with many responsibilities like taking care of memory management, versioning, CasPol etc.
DLR is new with .Net 4.0 which is the Dynamic Language Runtime and used to run the application on the fly wherever required. CLR runs as statically while DLR runs dynamically.

12. In case more than one version of an installable is installed, which version is invoked by default?
A. By default the CLR will take and invoke the latest version of the dll and execute it accordingly. There could be the same name assemblies exists in the GAC but they will have different versions altogether for their uniqueness.
So while running the application, CLR takes the latest version assembly and use in the application.

13. What are Globalization and localization? How to implement them?
A. Globalization is the concept of developing the application in more than one language while the Localization is used for a particular language. Like if we develop the application in more than one language we need to create the resource files (.resx) by using System. Globalization and when we open the application in a particular language, then the localizations used to convert that application to the selected language.

14. What is assembly, GAC? Where they are physically located?
A. Assembly is the collection of classes, namespaces, methods, properties which may be developed in different language but packed as a dll. So we can say that dll is the assembly.
There are 3 types of assemblies- Private Assembly, Shared Assembly, and Satellite Assembly.
GAC (Global Assembly Cache)- When the assembly is required for more than one project or application, we need to make the assembly with strong name and keep it in GAC or in Assembly folder by installing the assembly with the GACUtil command.
To make the assembly with strong name:
SN -k MyDll.dll
And to install it in GAC:
GacUtil -i MyDll.dll
GAC assemblies are physically stored in Assembly folder in the system.

15. How to configure HTTPS for a web application?
A. To configure the HTTPS (HTTP with Secure) for the web application, we need to have a client certificate. We can purchase the client certificate from the trusted providers and then we need to install that provider for our site. By implementing the HTTPS, all the data which is passing will be in encrypted format and will be more secure.

16. What are in-proc and out-proc? Where are data stored in these cases?
A. In-Proc and Out-Proc is the types of Sessions where the session data can be stored in the process memory of the server and in the separate state server.
When the session data is stored in the process memory of the server, the session is called as the In-Proc server. In this case when the server is restarted, the session data will be lost.
When the session data is stored in the separate server like in state server or in Sql Server, the type of session is called as the Out-Proc session. In this case, if the server where the application is running is restarted, the session will be still remain in the separate servers.
So in the in-Proc session state, the session data is stored in the Process memory of the Server where the application is running.
In the Out-proc session state, the session data is stored in the separate server- may be state server or in sql server.

17. When the View state is saved, and when is it loaded? How to enable/ disable View states?

A. View State data is stored in the current page in base64 encoded format. It gets loaded with the page and displays the values to the controls after the decoded. Internally it actually saves the check-sum of all the control data where the view state is enabled.so that when the page gets loaded due to any post back, it again finds the check-sum and then decodes the Base64 encoded string and gets back the same data to the controls. We can see the view state base 64 encoded string in View Source of the page. It will be like _VIEWETATE="DSDSDF8DGDGDFGFD5FDGGDJFF23BNN457M9UJOG"this.

View state won't take the client or server memory to keep the view state data.

18. Difference between GET and POST. Which one is more secure?
A. GET and POST methods are used for the data transfer between the web pages. GET mainly used for small data which is not secure because in case of GET method, the data which we are passing will be visible in the url so we can't keep the secure data which will be visible in the url. There is also limited data which can be passed in case of GET method (max 255 character).
POST is used for transferring the huge data between the pages where we can keep the secure data and can transfer it. In case of using the POST method, the data which is transferring between the pages will not be visible so it is more secure than the GET method. Also there is no limit for POST method to post the data to the next page.
POST is more secure.

19. What are Razor engines? How is it diff from ASP Engines?
A. RAZOR engine is the new concept in the MVC 3 which is mainly used to create the views in the MVC applications. It created the cshtml pages for the MVC application and cshtml pages can be generated automatically by using the Razor engine.ASP engine create the aspx pages while Razor engine creates the pages.

20. Pros and cons of JavaScript and AJAX.
A. JavaScript is a scripting language and mainly used for client side validation. We can validate the client side data before sending to the server. So by this we can improve the performance of the application.
Ajax is Synchronous JavaScript and XML which is used for the Asynchronous calls from the server. It uses internally the JavaScript for making the call and use XML for the Data Transfer. It basically uses the XmlHttpRequest for the asynchronous calls to the server and communicates with the XML data which is platform independent. So Ajax can be used with any technology.

21. In how many different ways can JavaScript be used/called in an application?
A. JavaScript can be used for Client Side validation, can also be used for calling of server side methods and functions, can be used for calling the web services etc.

22. What needs to be done to call a JavaScript function from code behind?
A. If we want to call the JavaScript function from the code behind, we need to attach the JavaScript to the events in the page_load event as:
protected void btnSave_cliekc9object sender, EventArgs e)
{
btnSave.Attributes.Add("onclick,"JavaScript: retrun Validatedata();");
}
Here ValidateData is the JavaScript function which can be used to validate the page data and if validation fails, it will return and will not execute the server side btnSave_click event.

23. Difference between Server Controls and User controls?
A. User controls are used for the re-usability for the controls in the application. By using the user control, we can use the same control in the various pages. User controls can be created by combining more than one control. To use the user controls, first we need to register them in the web page where we want to use that control. A separate copy is need in each page where we want to use the user control. User controls can't be included in to the toolbox.
Server controls are those controls which can be found in the toolbox and can be directly drag to the application like textbox, button etc. For the server control, only 1 copy of the control is needed irrespective of the number of web pages. If we want 10 text-boxes to be added in our web page, we need only 1 copy of the textbox in the toolbox and can be dragged 10 times.

24. Difference between Var, object and Dynamic types.
A. var is the keyword introduced with .net 3.5 and used to store any kind of data like data-set, data table, int, float, char etc. We can keep any kind of data in the var variable.
var myVar = new String[] {"hello", "world!!"} ;
Here the myVar is the var type variable which is used to store the string array. Like this we can store any type of data into the var.
Object is the type which is used to store the objects of any kind. These objects need to be type caste when required.
Like object mybject = "Hello"
Here the myObject variable of object type is used to keep the string variable. Now when we want this variable value, we need to typecast it like
string strvar= (string) myobject;
Dynamic- It’s a keyword introduces with the .net 4.0 and used to keep the data similar to the var keyword. The difference between the var and dynamic is that the dynamic variable uses the same memory location to store the object and not changes throughout the application.

25. Difference between Functions and methods.
A. in.Net terminology, both are same. in general, we use method in .net but in scripting language we use function like JavaScript function.
Here the difference can be Function always returns a value which method may or may not. It depends upon the return type of the method.

26. Difference between Abstract classes and Interface. Explain with scenario where to implement one?
A. Collection of the Abstract (Incomplete) and Concrete (complete) methods is called as the Abstract class. If there is at least one abstract method in a class, the class must be abstract class.
When there is the similar behavior, we can use the abstract class.
e.g. We want to calculate the area of few component. As this is not generic to the application. We have only few component- like Circle, Ellipse, parabola, Hyperbola, Triangle etc.
So we can create an abstract class and implement it like below:
public abstract class MyAbstractClass
{
// some other concrete members
public abstract void Area();// abstract member
}
Now in the child class, let’s say i have a circle class and want to calculate the area of the circle:
public class Cicle: MyAbstractClass
{
public override void Area()
{
// calculate the area of the circle
}
}
In the similar fashion, we can calcite the area of other shapes.
Collection of abstract members is called as the Interface. When the behavior is not similar, we need to use the interface. All the members of the interface
must be overrides in the child class.
e.g. Print functionality of the application can have an interface like:
interface Inf
{
void Print();
}
Now as this is the generic functionality and can be implemented in any of the page so we have taken it as interface. Now we can implement this functionality in to any page like:
class MyClass:Inf
{
public void print
{
// write details about the print
}
// Here we can implement any kind of print-like print to excel, xml, word all depends on the our decision.
}

27. Different forms of Polymorphism. Differences between Abstraction and Polymorphism.
A. Polymorphism is to use the same function in many forms. The polymorphism is of 2 types-
a. Classical polymorphism (Overloading)
b. AdHoc polymorphism (Overriding)
When the runtime (CLR) find the behavior of class members at the runtime of the program, it is called as the AdHoc polymorphism or Overriding.in this the method name is same but they are implemented in the different class. We use virtual keyword in the base class method to be overrides in the child class using the override keyword.
e.g.
public class MyClass
{
Public int Add(int a, int b)
{
Return a+b;
}
Public int Add(int a, int b, int c)
{
Return a+b+c;
}
}
When the run-time (CLR) find the behavior of class members at the compilation of the program, it is called as the Classical polymorphism or Overloading.in this the method name is same but there prototypes (parameters) are different and it is implemented in the same class.
e.g.
Public class MyBaseClass
{
Public virtual void Show(string message)
{
Console.WriteLine(“Your message is : ”+ message);
}
}
Public class MyChildClass: MyBaseClass
{
public override void Show(string message)
{
Console.WriteLine(“Your new message is : ”+ message);
}
}
Abstraction is the behavior to get the required functionality in the child class. So we don’t matter whatever is written in the base class. We only need to force the child class to implement my required functionality.
Abstract keyword is used to get the abstraction behavior.

28. What are Delegates and Events?
A. A Delegate is an object, which points to another method in the application. Delegate holds, name of the method, arguments of the method (if any) and the return type of the method.
See the below points regarding the Delegate:-
·          delegate keyword is sealed type in System. Multicast namespace.
·          Delegate works like a function pointer in C language.
·          Delegate holds the address of the function.
·          Delegate hides the actual information which is written inside the method definition.
·          A delegate can hold address of a single function as well as the address of multiple functions.
·          There are 2 types of delegate- Single-cast delegate (hold single function) and Multicast delegate(hold multiple functions).
·          Addition and subtraction are allowed for the delegates but NOT multiplication and division. It means, we can add delegates, subtract delegates etc.
e.g. To create a single cast delegate, first we can create a class with a method as:
public class DelegateDemo
{
public void Show(string msg)
{
Console.WriteLine(msg);
}
}
Now we can call the method Show using the delegate as:
public delegate void MyDelegate(string message); //declare delegate
now we need to create the object of the delegate with the address of the method as:
DelegateDemo obj = new DelegateDemo();//class object
MyDelegate md= new MyDelegate(obj.Show(“Hello World!!”));
md(); // call the delegate
We can create the events and event handler by using delegate with the below syntax:
public delegate void textChangedEventHandler(Object sender, TextEventArgs e);
This event handler will be used to handle the textbox text changed event.
We can get more details about the delegate and events from the below link:
http://msdn.microsoft.com/en-in/library/orm-9780596521066-01-17.aspx

29. Covariance and Contra-variance.
A. covariance and contravariance are the new features added with the .net 4.0. They are basically used for the implicit reference conversion for different .net types like array, delegate, and generic etc
You can go to the below link for more details with the examples that how we can use the covariance and contrvariance to implicate reference conversion:
http://blogs.msdn.com/b/csharpfaq/archive/2010/02/16/covariance-and-contravariance-faq.aspx

30. What are Extension methods?
A. Extension methods are special types of methods which are static methods but called as the instance methods. The extension methods are added with the .Net framework 3.5 and with the Visual Studio 2008.
These methods won’t affect the existing class and the label. These methods are used for the extra behavior which the calls can provide. There is no need to build the class again if we add any extension method to the class.
There are various inbuilt methods added in .Net 3.5 with the introduction of LINQ. We can see the extension methods like Order By when we use the Linq as:
e.g.
int[] numbers = { 10, 45, 15, 39, 21, 26 };
var orderedNumbers = numbers.OrderBy(a => a);

31. What are Anonymous methods and Lambda Expression?
A. Anonymous methods are those methods which does not have the name. As they don’t have the name, so there is no way to call these methods. These methods are created by using the work delegate as below:
button1.Click += delegate{listBox1.Items.Add(textBox1.Text)};
Lambda Expression: It’s an easy way to create anonymous functions. It is also an anonymous function which has the capability to contain expressions and statements. We can create the delegate and expression tree types using the lambda expression.
For more details regarding the anonymous method and lambda express, you can go through the below link:
http://www.codeproject.com/Articles/47887/C-Delegates-Anonymous-Methods-and-Lambda-Expression

32. Multithreading. How to implement Multithreading?
A. Executing more than one process simultaneously called as multithreading. To implement the multithreading concept, we need to use the System. Threading .dll assembly and the System. Threading namespace.
To write the thread program, we need to create a class with the method. Now we can create the thread object and then pass the method by using the class object to the method.
After that we need to create the ThreadStart delegate which will call the actual method of the class.
You can go through below link for more explanation and other details regarding the implementation and the code snippet:
http://www.codeproject.com/Articles/1083/Multithreaded-Programming-Using-C

33. Which interface is used to-
a.         Convert Boolean values to Visibility values?
b.         Compare two integer values?
c.          Compare String values?
A. Check the below interfaces which are used in these scenarios:
a.         Convert Boolean values to Visibility values?
b.         Compare two integer values?- IComparable interface
c.          Compare String values? IComparer interface

SQL Server

34. What is the difference between a View and a Cursor?
A. View: It is one of the database object which is also called as virtual table. We can also say that it is a window through which we can see some part of database. View is also called as stored query because we are going to fetch some data using View.
View doesn’t contain any data. It’s just a virtual table which is used to get the records from the base table for which the view is created. View is faster than ad hoc queries because when we create the view and execute it once. Next time onwards it will be available as the compiled format. So whenever the view is called, it will just execute rather than compiling.
Cursor: Cursor is a database object which is also the buffer area which is created as a result of any sql statement to hold the intermediate values.
Views are used to format the rows individually. By using the views, we can process the individual rows. There are 4 types of cursors in Sql Server-
a.         Static Cursor
b.         Dynamic Cursor
c.          Key set cursor
d.         Read-only cursor

35. How to execute multiple update on different conditions in a single query?
A. To execute multiple update using a single Sql update statement is the new feature available with the SQL Server 2008. In this, we can update multiple rows using a single update command.

36. Left outer joins and Right Outer joins
A. Joins are used to join 2 or more tables using some conditions. There are 3 types of Joins in SQL Server database-
a. Left Outer Join
b. Right Outer Join
c. Full Join
In order to extract the matched row from both the tables and unmatched row from the first table, left Outer join is used. The syntax for left outer join condition is:
T.Col1* = T2.Col1
In order to extract the matched row from both the tables and unmatched row from the second table, right Outer join is used. The syntax for right outer join condition is:
T.Col1 = *T2.Col1
In order to extract the matched row from both the tables and unmatched row from the first table and then unmatched row from the second table, full join is used. The syntax for full join condition is:
T.Col1* = *T2.Col1

37. Exception handling.
A. Exception Handling is the way to handle the unexpected error. From the SQL Server 2005 version, try…catch block is also supported to catch the exceptions in SQL Server database. There is various other ways to catch the error like @@Error which is the global variable and used to get the error. RaiseError is another inbuilt method which is used to display the error.

38. What is Performance Tuning? How do you implement it.
A. Performance Tuning is the process through which we can optimize the SQL Server objects like functions, triggers, stored procedure so that we can achieve high response time to the front end. In the performance tuning process we generally check for the below point and optimize the objects processing:
a. Through Query Execution plan, check for the processing time of the query execution.
b. Check the join conditions and break all the condition for executions of the queries individually
c. Check for the error prone process, conditions in the queries.
d. Check for the loops whether they are terminated if any error occurs
e. Check for the processes which are taking more time in execution and how to reduce the response time.

39. Difference between Having and Where clauses.
A. When the where clause is not able to evaluate the condition which consists of group functions, Having clause is used. Having clause is always followed by the Group By clause.
Where clause is used to filter the records based on the conditions. If there is the requirement to get the group data in the select statement and where clause is not able to get it, we can use the Having clause.
e.g. Display DeptNo, No.of Employees in the department for all the departments where more than 3 employees are working
SELECT DEPTNO, COUNT(*) AS TOTAL_EMPLOYEE
FROM EMP
GROUP BY DEPTNO HAVING COUNT(*) >3

40. Difference between Temp tables and Tables variables?
A. Temp Table in SQL Server:
a. Temp table is the special type of tables which are used to store the intermediate data of the actual table.
b. Temp tables are only visible to the current sessions of the sql server instance. When the session end, these table data automatically drops.
c. We can’t join the temp tables as they don’t allow the foreign key constraints.
d. Temp tables are created in TempDB database.
e. We can use the same temp table name for the different user sessions.
f. Mostly used in stored procedure to handle the intermediate data.

41. What does @ and @@ suffixed by property names specify?
A. @- This is used for the variable declaration
e.g. @name varchar2(50)
@@- This is used for the Global variable declaration
e.g. @@Error=0

42. Self-join queries.
A. Self-Join is a type of join which is used to join the same table by creating the second instance of the same table. So we join 2 instances of the same table in case of self-join. This type of join is used when there is the requirement to get the referenced data which is available in the same table.
e.g. A table contains EmpId, Ename and ManagerId
As the manager id is also an employee id. Now if we want that who is the manager of which employee. In this situation, we need to create the instance of the same table and get the required data as:
SELECT EMPID, ENAME, ENAME AS [MANAGER NAME]
FROM EMP E1, EMP E2
WHERE E1.EMPID= E2.MANAGERID

43. Types of Index.
A. Indexes are one the database objects which is used to improve the performance of the database queries. it reduces the table scan while retrieving the data from the database and the search gets fast-
There are 2 types of indexes used in the SQL server:
a. Clustered index
b. Non clustered index
There are 3 more types of index but those comes under the above two-
a. unique index
b. Composite Index
c. XML Index-added in SQL Server 2005
The index basically works on searching like binary tree where the root value is the finding value and it will be compared with the partitioned value of the tree.

44. Difference between Primary key, Unique key and Candidate key?
A. Primary Key- It is a key to make the unique identification of the row in a table. It doesn’t allow null values in the primary key column. We can create the lookup columns based on the primary key. One table allows maximum of 1 primary key and in 1 table, we can create the primary key column by using 16 columns. Due to one of the normalization rule, we have to create primary key for the table to make the rows unique.
Unique Key:- Primary Key+ Not null is called as unique key. Unique key is also used to make the rows as unique in a table. The only difference between primary key and unique key is that primary key doesn’t allow null value while the unique key allow. The limitation of the null in unique key is that it allows only one Null so in only one row; we can make the key as null for the unique key.
Candidate key- the key other than primary key to make the rows as unique is called as candidate key. In candidate key, we take the columns which are not in the primary key and make the key for uniqueness of the row.

45. What is the default value for Date type. What are Min and Max values for Date in 2008.
A. The default value of Date is CURRENT_TIMESTAMP
Below are the new date and time values in Sql Server 2008:
In SQL Server 2008:
1. DateTime2
Min Value: 0001-01-01 00:00:00.0000000
Max Value: 9999-12-31 23:59:59.9999999
2. Date
Min Value: 0001-01-01
Max Value: 9999-12-31

You can go through the below link for couple of work around:
http://dhaneenja.blogspot.in/2008/06/minimum-year-value-in-sql-server.html

WCF

46. What is WCF also known as?
A. WCF (Windows Communication Foundation) is also know an Indigo by its code name.

47. Difference between WCF and Web Services?
A. Below are the main differences between the WCF and Web Service:
Web Service:
a.    Can be hosted in IIS only
b.    Only two types of operations affects- One-Way, Request-Response
c.     To serialize the data use System.Xml.Serialization
d.    To encode the data use- XML 1.0, MTOM, DIME, Custom
WCF service:
a.    Can be hosted in IIS, Self Hosting, WAS, Windows Services etc
b.    Three types of operations affects- One-Way, Request-Response and Duplex
c.     To serialize the data use System.Runtimel.Serialization
d.    To encode the data use- XML 1.0, MTOM,Binary, Custom
e.    WCF Service can be accessed through HTTP, TCP, Named pipes, MSMQ,P2P etc.

48. What are Endpoints?
A. The collection of Address, Binding and Contract is called as End Point. In Sort,
EndPoint = A+B+C
Address (Where)- it means where the service is hosted. URL of the service shows the address.
Binding (How)- How to connect to the service, is defined by the Binding. It basically has the definition of the communication channel to communicate to the WCF service
Contract (what)- It means what the service contains for the client. What all the methods are implemented in the WCF service is implemented in the Contract.

49. What are Behavior and Bindings?
A. Binding mainly describes about the communication of the client and service. For this, there are protocols corresponding to the binding behavior which will take care of the communication channel. There are different protocols which we use for the different types of bindings. E.g. HTTP, TCP, MSMQ, Named Pipes etc.
Behavior is used for the common configurations that could be for endpoints. When we use the common behavior, they affect to all the end points. Adding the service behavior affect the service related stuff while the endpoint related behavior affects the end points. Also operations level behavior affects the operations.

50. What are different types of Contracts supported?
A. There are mainly 5 type of contracts used in WCF service:
a. Service Contract
b. Operation Contract
c. Data Contract
d. Message Contract
e. Fault Contract

51. What is the difference between Transport and Message Security mode?
A. WCF supports 2 types of security- Transport Level Security and Message Level Security
Transport Level Security- In this type of security, we make the transport channel as secure so that the data flows in that channel will be automatically secured. For HTTP channel, we use the client certificate for the security of the web address. SSL is used for the HTTP channel security. As we don’t need to secure each of the messages which are floating between the client and the service, the speed is faster as direct message is going to the client from the service.
Message level security- This type of security in WCF is used where we don’t have the fixed transport medium and we need to secure each message which is floating between the server and the client. In this type of security we use certain algorithms for making the message as secure message. We use some extra bits and send with the message. We also use some encryption techniques like SHA1 or MD5 which make the proper security for our message. As each message needs to be secured, this type of security makes some delay in the process of sending and receiving the messages.

52. How to configure WCF security to support Windows authentication?
A. To support the WCF security in Windows Authentication, we need to add the ClientCredetialType attribute to “Windows” under the security tab element:
transport clientCredentialType="Windows"

53. How to use Fault Contract?
A. Fault Contract is mainly used for viewing and displaying the errors which occurred in the service. So it basically documents the error and the error message can be shown to the user in the understandable way. We can’t use here the try….catch block for the error handling because the try…catch is the technology specific (.Net Technology). So we use the Fault contract for the error handling.
e.g. To use the Fault contract, we can simply write like the below:
public int Add(int number1,int number2)
{
// write some implementation
throw new FaultException (“Error while adding data..”);
}
Here the fault Exception method is the inbuilt method which will throw the exception and display the message . We can use the custom class so that the message can be customized and the customized message can be sent to the client.
So we can creeat a clss like:
Public Class CustomException()
{
public int ID{get;set;}
public string Message{get;set;}

public string Type{get;set;}
}
Now this custom type we ca use with the Operation Contract as:
[ServiceContract]
Public interface IMyInterface
{
[OperationContract]
[FaultContract(typeOf(CustomException))]
Int Add(int num1,int num2);
}
Now while implementation of the Add method, we can assign the class properties.

WPF

54. Diff between XML and XAML.
A. XAML is the declarative XML based language which is used to define the objects and properties. XAML document is loaded by XAML parser. So XAML Parser initiates the objects and set those properties. XAML is mainly used in creating the objects in WPF and Silverlight applications.
For more detailed explanation, you can go through the below link:
http://www.differencebetween.net/technology/software-technology/difference-between-xml-and-xaml/

55. Stack Panel and Wrap Panel.
A. StackPanel is one of layout control in WPF. We can place the child controls inside the stack panel either horizontally or vertically. So it provides two types of orientations- Horizontal Orientation and Vertical orientation.
You can go through the below link for more detailed explanation and the code snippet:
http://wpftutorial.net/StackPanel.html

Wrap panel is another layout control which is similar to the StackPanel. Wrap panel not only keep the control in horizontal and vertical orientation but also wrap them in to new line if there is no space. Here also the orientation can be set as Horizontal or Vertical. Its main use is to arrange the tabs in the tab control, menu control or in toolbar items.
You can go through the below link for more details:
http://wpftutorial.net/WrapPanel.html

56. Hierarchical Data Template.
A. Hierarchical Data Template is a type of data template which is used to bind the controls which supports HeaderedItemsControl, like TreeViewItem or MenuItem
We can bind those controls items using the Hierarchical Data Template. It displayed the data in to Hierarchical structure in the tree structure. It could be in the left to right or top to bottom.
You can go through the below link for more details:
http://msdn.microsoft.com/en-us/library/system.windows.hierarchicaldatatemplate.aspx

57. Virtualization.
A. This is the feature in WPF which increases the efficiency of the programs when there are the large data objects. If the WPF ItemsControl is bound with the large collection data source object and we enabled the virtualization, then the controls will show only the data which is in the visual container for those items which are visible currently. This visual data is only the small part of the large data object. Now when the user will scroll down or up, the rest of the data will be visible and previous data will be hidden again. So this is increase the efficiency of the program from the UI prospective.

58. Events and Routed Events.
A. Routed event is special type of event which can invoke and handle multiple events from different objects rather than the event which is coming from one object. So it generally handles the object from the element tree. So whatever the elements inside the element tree and if they generate the event-may be multiple events, the routed event is capable of handling those events.
The routed event can be invoked in both the directions but in general it comes from the source element and then bubbled up in the element tree until the root element.

59. Bubbling and Tunneling.
A. Bubbling: When the events are raised form the innermost element in the visual tree and comes up towards the root element, is called as bubbling.
Tunneling: It is the opposite process of Bubbling where the events fired by the root element goes down towards the last child element control.
Please go through the below link for more details:
http://www.dotnetspider.com/forum/130497-event-bubbling-event-tunneling.aspx

60. Resource Dictionary, Static Resources and Dynamic Resources.
A. Static and Dynamic resources are used for binding the resources to the control objects.
The main difference between StaticResource and DynamicResource is that how the resource is retrieved elements. If the resource is StaticResource, it will be retrieved only once by the element whoe is referencing it and it will be used for all the resources. While the DynamicResource gets its value each time they reference to the objects. So StaticResource is faster than the DynamicResource , because StaticResource needs to get the value only once while the DynamicResource needs each time to get it.

61. What is Prism?
A. Prism is the framework or the set of guidelines which is used to develop the WPF desktop application as well as the Silverlight Rich Internet applications. So it’s a kind of Design pattern to Develop the XMAL based application. It also used to develop the Windows 7 applications. Prism mainly helps to design the loosely coupled components which can be easily integrated with the other components of the overall application. Prism mainly used to build the composite applications which need various other components to be integrated.
Prism mainly guides of creating the applications using the Model-View-ViewModel (MVVM) model, Managed Extensibility Framework (MEF), and navigation in the application.
To use the Prism framework, we need to use their library called as Prism Library. So prism Library is the inbuilt set of components which can be used in developing the WPF and Silverlight applications.
You can go through the below link for more details and the use of the components of the Prism framework:
http://msdn.microsoft.com/en-us/library/ff648465.aspx

62. Dependency Injection, Event Aggregator.
A. For the details about the dependency injection, you can follow the below link:
http://wpftutorial.net/ReferenceArchitecture.html
EventAggregator : It is the utility service which contains the events and allows the decouple the publisher and subscriber so that they can be buildup independently. Decouple is primarily useful when a new module needs to be added or removed or modified. The new module can be added as per the event fired and defined in the shell.
For more details about the Event Aggregator, you can follow the below link:
http://msdn.microsoft.com/en-us/library/ff921122(v=pandp.20).aspx

63. Shell, Bootstrapper and Region Managers
A. Bootstrapper:- An utility in WPF engine which is mainly responsible for the initialization of the application by using the composite application library. By using the bootstrapper we can find out how the components of the application are wired up in the composite application library. The bootstrapper responsibility to create the Shell or main window. Composite application library has the default abstract class UnityBootstrapper which actually handles the initialization.
You can go through the below link for more details about the bootstrapper:
http://msdn.microsoft.com/en-us/library/ff921139(v=pandp.20).aspx
Region and Region Managers: This is concept of Prism framework. We define the region through XAML code and once a region is defined, automatically it will be registered with the RegionManager. Actually the Bootstrapper registers a service called the RegionManager at run time. RegionManager is a dictionary where the key is name of the region. The value of the key is the reference of the IRegion interface. RegionAdapter is used to create the instance reference of the IRegion interface.
You can go through the below link for more details about the Region and Region Manager:
http://msdn.microsoft.com/en-us/magazine/cc785479.aspx#id0090091

64. What are MEF and Unity?
A. The MEF (Managed Extensibility Framework) is the new concept in .net 4.0. It is used to create the lightweight and extensible applications to create Managed Extensibility Framework. It is not only allows the extension but also reused within the application. Extension can be easily encapsulating the code using the MEF.
For more details, you can go through the below link:
http://msdn.microsoft.com/en-us/library/dd460648.aspx

65. How to navigate to another page?
A. There is a class NavigationService which can be used for navigation of the WPF window:
this.NavigationService.GoForward();
//or
this.NavigationService.Navigate("MysecondPage.xaml")

66. What is the difference between IEnumerable and IQueryable?
Ans. IEnumerable and IQuerable are used to query data from database and collections. The IEnumerable is basically inherited from IQueryable, so it’s having all the features of the IQueryable in addition to its having additional own features.

S.No	IEnumerable	IQueryable
1.	Exists in System.Collections Namespace	Exists in System.Linq Namespace
2.	Can move to forward only in the collection.	Can move to forward, backward or in between the items.
3.	Best for collection like List, Array or in-memory collection	Best for the collections which is out memory like services, remote databases etc
4.	Suitable for LINQ to Objet and Linq to XML queries.	Suitable for Linq to SQL queries
5.	It doesn’t supports custom query, Lazy loading so it’s not good for paging scenarios.	It supports custom query using CreateQuery and Execute methods. Also support lazy loading so good for the paging scenarios.
6.	The extension methods which supports be IEnumrable takes the functional objects as the parameters.	The extension methods which supports be IEnumrable takes the expression tree expressions as the parameters.

In the first example (By using the IEnumerable), the generated SQL is as below:

In the second example (By using the IQueryable), the generated SQL is as below:

We can see that by using the IQueryable, the performance will increase as it has the TOP clause in the query.

67. What is cross site scripting? (XSS)

Ans. Cross-site scripting is the way to attacks and insert the vulnerabilities in Web page. This attack is injected by client-side code. The script which is inject by the client can embed itself in response data. The response data which send back to the malicious user. The browser can’t recognize the scripts as it is responded from the trusted source.

The cross-site scripting attacks also work on the HTTP and HTTPS.

There are 2 ways to prevent the cross site scripting attack:

Constrain input- Validate the input length, type, formatting, range etc

Encode output- Send the input data with encode e.g. Encode to HTML
To prevent the cross-site attack, we can set the below attributes in web.config file:

68. If I want to see my website similar in all the browsers then what I need to do for that?

Ans. If you want to see the website with the same look and feel then you need to write the common css style which should be same for all browsers. Actually every browser will not support every css elements so it is not possible to use the same css to support all the browsers. You need to write the common css elements in the file and then apply it across the website. Else you need to write the separate css file as per the browser.

69. If say 1 Lac users are using any particular website then what you will do to prevent crashing of server? Which care you will take at the time of coding?

Ans. There are the ways like we can have multiple servers to handle the requests from the users. In this, we can have the Web Gardening concept where we can have the multiple web servers and then one main server to handle the number of requests and switch the requests to other servers.

70. Why to use design patterns?

Ans. Design Pattern is the way to solve the recurring problems which occur during the designing of the applications. As the requirements increases, the projects becomes complex and due to the complexity, it’s difficult to maintain it.

With the help of design patterns, we can reduce the complexity and with the help of OOPs paradigm, we can make our applications more efficient in all the ways.

According to the GoF (Gang of Four) company, the Design Patterns can be classified to 3 ways:-

Creational Design Pattern
Behavioral Design Pattern
Structural Design pattern

71. If I have a class C and two interfaces I1 and I2 and I have add method inside I1 and I2 then how to specify which one has to be called?

Ans. By using the explicit implement interface, we can implement the same method which is defined in both the interfaces.

e.g.

The implementation will be as below:

72. Garbage collection uses which type of algorithm? How it will find which object is unused?

Ans. Mark-And-Release is the algorithm which the garbage collection uses to reclaim the memory of the unreferenced objects which are no longer used.

The algorithm Mark-and-Release work in 2 steps:-

a. In the first steps, it marks all the accessible objects of the heap memory. This is called as mark phase.

b. In the second step, scan the heap and reclaim all the unmarked objects by the Garbage Collection algorithm. This step is called as sweep phase.

Below are the algorithm steps:

For the detailed description, follow the below link:

http://www.brpreiss.com/books/opus5/html/page424.html

73. What is the difference between out and ref?
Ans: Ref and Out are the parameters which are used in the methods [ref] and [out] both allows the called method to modify a parameter. The difference between them is what happens before you make a call.

[ref] means that the parameter has a value on it before going into the function. The called function can read and or change the value any time. The parameter goes in, then comes out
[out] means that the parameter has no official value before going into the function. The called function must initialize it. The parameter only goes out.

So the main difference between the ref and out parameter is that the out parameter doesn't needs to be initialized while the ref parameter must be initialized before passing to the function.

74. Is it possible to use more than one out parameter?

Ans. As we know that the method always returns a single value but by using the out parameter, we can return multiple values from the method or function.

In C# we can write the small code snippet which will describe to return the multiple values using the out parameters:

We can also use the struct which will contain the multiple values as the return:

There is another way to return multiple values like using Tuple class (newly introduces in .Net 4.0). The tuple class can return the object which can contain multiple values in it.

75. Is it possible to use .js files used under script will be in body and not in header? Why?

Ans. The .js file is used in header because first the .js file should be loaded to the application and then rest of the content should be load.

Dotnet Interview Questions

2014-06-24T03:08:00.002-07:00

1.) What is asp.net life cycle ?
Life Cycle Events

PreInit

The properties like IsPostBack have been set at this time.

This event will be used when we want to:

Set master page dynamically.
Set theme dynamically.
Read or set profile property values.
This event is also preferred if want to create any dynamic controls.

Init

Raised after all the controls have been initialized with their default values and any skin settings have been applied.
Fired for individual controls first and then for page.

LoadViewState

Fires only if IsPostBack is true.
Values stored in HiddenField with id as _ViewState decoded and stored into corresponding controls.

LoadPostData

Some controls like:

Fires only if IsPostBack is true.
Some controls like Textbox are implemented from IPostBackDataHandler and this fires only for such controls.
In this event page processes postback data included in the request object pass it to the respective controls.

PreLoad

Used only if want to inject logic before actual page load starts.

Load

Used normally to perform tasks which are common to all requests, such as setting up a database query.

Control events

This event is fired when IsPostBack is true.
Use these events to handle specific control events, such as a Button control's Click event or a TextBox control's TextChanged event.

PreRenderRaised after the page object has created all the controls that are required for rendering which includes child controls and composite controls.

Use the event to make final changes to the contents of the page or its controls before the values are stored into the viewstate and the rendering stage begins.
Mainly used when we want to inject custom JavaScript logic.

SaveViewState

All the control values that support viewstate are encoded and stored into the viewstate.

RenderGenerates output (HTML) to be rendered at the client side.

We can add custom HTML to the output if we want here.

Unload

Fired for individual controls first and then for page.

2. Used to perform cleanup work like closing open files and database connections.

2.) How the request is handled by IIS ?

We give an URL to an aspx page in the browser address bar and press enter. What happens next? We get the response in terms of rendered HTML but how?

We are requesting something from the browser, which means indirectly we are requesting something from the Web Server, that means IIS. IIS, based on the file extension, decides which ISAPI extension can serve the request.

And in case of ASP.Net (.aspx) it will be aspnet_isapi_dll so the request is passed to it for processing.
When the first request comes to the website,

an application domain is created by the ApplicationManager class where exactly the website runs, and which creates an isolation between 2 web applications.
Within the application domain an instance of the HostingEnvironment class is created which provides access information about the application such as the name of the folder where the application is stored.
Next ASP.Net creates core objects like HttpContext, HttpRequest,HttpResponse.
Finally the application starts by creating an instance of the HttpApplication Class (which can be reused for multiple requests to maximize performance).

3.) What is Difference between Session and Cookies ?

The basic and main difference between cookie and session is that cookies are stored in the user's browser but sessions can't store in user's browser. This specifies which is best used for.

• A cookie can keep all the information in the client's browser until deleted. If a person has a login and password, this can be set as a cookie in their browser so they do not have to re-login to your website every time they visit. You can store almost anything in a browser cookie.

• Sessions are not reliant on the user allowing a cookie. They work like a token in the browser which allowing access and passing information while the user has opened his browser. The problem in sessions is when you close the browser the session will automatically lost. So, if you had a site requiring a login, this couldn't be saved as a session but it can be saved as a cookie, and the user has to re-login every time they visit.
cookies are nothing but a small piece of information on the client machine. before we create a cookies we should check whether the cookies are allowed at the browser side. They are limited in a size 4k.(they are 2 types of cookies peristant cookie , and session cookies)

Sessions cookies are stored in a server memory during the client browser session.When the browser is closed the session cookies are lost.

4.) Advantages and disadvantages of Session?

Following are the basic advantages and disadvantages of using session. I have describe in details with each type of session at later point of time.

Advantages:

It helps maintain user state and data all over the application.
It is easy to implement and we can store any kind of object.
Stores client data separately.
Session is secure and transparent from the user.

Disadvantages:

Performance overhead in case of large volumes of data/user, because session data is stored in server memory.
Overhead involved in serializing and de-serializing session data, because in the case of StateServerand SQLServer session modes, we need to serialize the objects before storing them.

Besides these, there are many advantages and disadvantages of session that are based on the session type. I have discussed all of them in the respective sections below.

5). What is state management?
Ans: State management is the process by which you maintain state and page information over multiple requests for the same or different pages.

6). Http is stateless, What does this mean?
Ans: Stateless protocol is a communications protocol that treats each request as an independent transaction that is unrelated to any previous request so that the communication consists of independent pairs of requests and responses.

7). What is Session?
Ans: We know that Http is stateless, means when we open a webpage and fill some information and then move to next page then the data which we have entered will lost.
It happed do to Http protocol stateless nature. So here session come into existence, Session provide us the way of storing data in server memory. So you can store your page data into server
memory and retrieve it back during page postbacks.

8). What are the Advantage and disadvantage of Session?
Ans: Advantages:
Session provide us the way of maintain user state/data.
It is very easy to implement.
One big advantage of session is that we can store any kind of object in it. :eg, datatabe, dataset.. etc
By using session we don't need to worry about data collesp, because it store every client data separately.
Session is secure and transparent from the user.
Disadvantages:
Performance overhead in case of large volumes of data/user, because session data is stored in server memory.
Overhead involved in serializing and de-serializing session data, because in the case of StateServer and SQLServer session modes, we need to serialize the objects before storing them.

9). What is Session ID in Asp.net?
Ans: Asp.Net use 120 bit identifier to track each session. This is secure enough and can't be reverse engineered. When client communicate with server, only session id is transmitted, between them. When client request for data, ASP.NET looks on to session ID and retrieves corresponding data.

10). By default where the sessions ID's are stored ?
Ans: By default, the unique identifier for a session is stored in a non-expiring session cookie in the browser. You can specify that session identifiers not be stored in a cookie by setting the cookieless attribute to true in the sessionState configuration element.
We can also configure our application to store it in the url by specifying a "cookieless" session
The ASP Session cookie has this format:-
ASPSESSIONIDACSSDCCC=APHELKLDMNKNIOJONJACDHFN

11). Where does session stored if cookie is disabled on client’s machine?
Ans: If you want to disable the use of cookies in your ASP.NET application and still make use of session state, you can configure your application to store the session identifier in the URL instead of a cookie by setting the cookieless attribute of the sessionState configuration element to true, or to UseUri, in the Web.config file for your application.
The following code example shows a Web.config file that configures session state to use cookieless session identifiers.

Code:

<configuration>
  <system.web>
    <sessionState 
      cookieless="true"
      regenerateExpiredSessionId="true"
      timeout="30" />
  </system.web>
</configuration>

12). Can you describe all the property set in web.config under session state?
Ans:

Code:

<configuration>
  <sessionstate 
      mode="inproc"
      cookieless="false" 
      timeout="20" 
      sqlconnectionstring="data source=127.0.0.1;user id=<user id>;password=<password>"
      server="127.0.0.1" 
      port="42424" 
  />
</configuration>

Mode: The mode setting supports three options: inproc, sqlserver, and stateserver. As stated earlier, ASP.NET supports two modes: in process and out of process. There are also two options for out-of-process state management: memory based (stateserver), and SQL Server based (sqlserver). We'll discuss implementing these options shortly.
Cookieless: The cookieless option for ASP.NET is configured with this simple Boolean setting.
Timeout: This option controls the length of time a session is considered valid. The session timeout is a sliding value; on each request the timeout period is set to the current time plus the timeout value
Sqlconnectionstring: The sqlconnectionstring identifies the database connection string that names the database used for mode sqlserver.
Server: In the out-of-process mode stateserver, it names the server that is running the required Windows NT service: ASPState.
Port: The port setting, which accompanies the server setting, identifies the port number that corresponds to the server setting for mode stateserver.

13). What are Session Events?
Ans: There are two types of session events available in ASP.NET:
Session_Start
Session_End
You can handle both these events in the global.asax file of your web application. When a new session initiates, the session_start event is raised, and the Session_End event raised when a session is abandoned or expires.

14). How you can disable session?
Ans: If we set session Mode="off" in web.config, session will be disabled in the application. For this, we need to configure web.config the following way:

Code:

<configuration>
  <sessionstate  Mode="off"/>
</configuration>

15). If I have more than one version of one assemblies, then how will I use old version (how/where to specify version number?) in my application?

Ans.The version number is stored in the following format: …. The assembly manifest can then contain a reference to which version number we want to use.

16). How do you create threading in.NET? What is the namespace for that?
Ans.
System.Threading;

//create new thread using the thread class’s constructor

Thread myThread = new Thread(new ThreadStart (someFunction));

17). What do you mean by Serialize and MarshalByRef?

Serialization is the act of saving the state of an object so that it can be recreated (i.e deserialized) at a later date.
The MarshalByRef class is part of the System.Runtime.Remoting namespace and enables us to access and use objects that reside in different application
domains. It is the base class for objects that need to communicate across application domains. MarshalByRef objects are accessed directly within their own
application domain by using a proxy to communicate. With MarshalByValue the a copy of the entire object is passed across the application domain

18). What is the difference between Array and LinkedList?
An array is a collection of the same type. The size of the array is fixed in its declaration.
A linked list is similar to an array but it doesn’t have a limited size.

19). What is Asynchronous call and how it can be implemented using delegates?

A synchronous call will wait for a method to complete before program flow is resumed. With an asynchronous call the program flow continues whilst the method executes.

//create object
SomeFunction objFunc = new SomeFunction();

//create delegate
SomeDelegate objDel = new SomeDelegate(objFunc.FunctionA);

//invoke the method asynchronously (use interface IAsyncResult)
IAsyncResult asynchCall = SomeDelegate.Invoke();

20). How to create events for a control? What is custom events? How to create it?
Ans.
An event is a mechanism used in a class that can be used to provide a notification when something interesting happens. (typical evens in a windows application
include: change text in textbox, double click or click a button, select an item in dropdown box).
A custom event is an event created by the user that other developers can use. For example assuming that we have a CashTransaction class and we have a bank
balance property in that class. We may want to set-up an event that provides a notification when the bank balance drops below a certain amount. In order to
produce an event the process would be roughly as follows:
Create the class for the event derived from EventArgs.
Create a delegate with a return type of void.
Create a class containing the method that will activate the event.
Create a class with methods to handle the event.

21). If you want to write your own dot net language, what steps you will you take care?

We will need to ensure that the high level code is compiled to MSIL (Microsoft intermediate language) so that it can be interpreted by the CLR.

22). Describe the diffeerence between inline and code behind - which is best in a loosely coupled solution?

The term ‘code behind’ refers to application code that is not embedded within the ASPX page and is separated out into a separate file which is then referenced
from the ASPX page. Inline code is the traditional ASP architectural model where business logic code was embedded within the ASP page. Separating the business
logic code from the presentation layer offers several advantages:
1) It allows graphic designers and web developers to work on the presentation layer whilst the application developers concentrate on the business logic.
2) The codebehind file is compiled as a single dll increasing the efficiency of the application,
3) The codebehind model offers a true OO development platform,
4) It speeds up development time as it allows developers to fully maximise the features of the .NET framework such as Cahing, ViewState, Session, Smart Navigation etc.
5) Code is much easier to maintain and susceptible for change.
6) The compiler and VS.NET provides much better support for error checking, intellisense and debugging when using the code behind model.

23). How dot net compiled code will become platform independent?

The raison d’etre for .NET was to cater for multiples languages on a single windows platform whereas the aim of Java was to be a single language on multiple
platforms. The only way that .NET can be platform independent is if there is a version of the .NET framework installed on the target machine.

24). Without modifying source code if we compile again, will it be generated MSIL again?
Ans.No.

25). How does you handle this COM components developed in other programming languages in.NET?

Ans.
use TlbImp.exe to import the COM types into your .NET project. If no type library for the COM component then use System.Runtime.InteropServices
use RegAsm.exe to call a .NET developed component in a COM application.

26). How CCW (Com Callable Wrapper) and RCW (Runtime Callable Wrappers) works?

CCW: When a COM application calls a NET object the CLR creates the CCW as a proxy since the COM application is unable to directly access the .NET object.
RCW: When a .NET application calls a COM object the CLR creates the RCW as a proxy since the .NET application is unable to directly access the .COM object.

27). What are the new thee features of COM+ services, which are not there in COM (MTS)?

Role based security.
Neutral apartment threading.
New environment called context which defines the execution environment

28). What are the differences between COM architecture and.NET architecture?

.Net architecture has superseded the old COM architecture providing a flexible rapid application development environment which can be used to create windows,
web and console applications and web services. .NET provides a powerful development environment that can be used to create objects in any .NET compliant language.
.NET addresses the previous problems of dll hell with COM by providing strongly named assemblies and side-by-side execution where two assemblies with the same name can run on the same box.

29). Can we copy a COM dll to GAC folder?

Ans.
No. It only stores .NET assemblies.

30). What is Shared and Repeatable Inheritance?

Shared Inheritance-: Shared Inheritance-: ITt is multiple times using same class. The mechanism of deriving a new class from an existing class is called inheritance. Shared inheritance introduces a new opportunity of ambiguity and additional implementation complexity. Assume D inherits from B and C, both of which inherits from A. Here A in shared. Single copy made from both derived classes is called shared inheritance.

31). Can you explain what inheritance is and an example of when you might use it?

Ans.
Inheritance is a fundamental feature of any OO language. It allows us to inherit the members and attributes from a base class to a new derived class. This
leads to increased code reusability and also makes applications easier to develop, maintain and extend as the new derived class can contain new features not
available in the base class whilst at the same time preserving the attributes inherited from the base class.

32). How can you write a class to restrict that only one object of this class can be created (Singleton class)?

Ans.
Use the singleton design pattern.

public sealed class Singleton
{
   static readonly Singleton Instance=new Singleton();
      static Singleton()
      {
      }
      Singleton()
      {
      }
      public static Singleton Instance
      {
           get
           {
                return Instance;
           }
      }
}

33). What are virtual destructures?

A constructor can not be virtual but a destructor may. Use virtual destructors when you want to implement polymorphic tearing down of an object.

  34). What is close method? How its different from Finalize and Dispose?

finalise is the process that allows the garbage collector to clean up any unmanaged resources before it is destroyed.
The finalise method can not be called directly; it is automatically called by the CLR. In order to allow more control over the release of unmanaged resources
the .NET framework provides a dispose method which unlike finalise can be called directly by code.
Close method is same as dispose. It was added as a convenience.

35). What is Boxing and UnBoxing?

Ans.
Boxing is the process of converting a value type to a reference type. More specifically it involves encapsulating a copy of the object and moving it from
stack to heap. Unboxing is the reverse process.

36). What is check/uncheck?

Ans.
checked: used to enable overflow checking for arithmetic and conversion functions.
unchecked: used to disable overflow checking for arithmetic and conversion functions

  37). What is the use of base keyword? Tell me a practical example for base keyword’s usage?

Ans.
The base keyword is used to access members of the base class from within a derived class:
* Call a method on the base class that has been overridden by another method.
* Specify which base-class constructor should be called when creating instances of the derived class.

A base class access is permitted only in a constructor, an instance method, or an instance property accessor.
It is an error to use the base keyword from within a static method.
Example:In this example, both the base class, Person, and the derived class, Employee, have a method named Getinfo. By using the base keyword,
it is possible to call the Getinfo method on the base class, from within the derived class.
// keywords_base.cs
// Accessing base class members

using System;
public class Person
{
protected string ssn = "444-55-6666";
protected string name = "John L. Malgraine";
public virtual void GetInfo()
{
Console.WriteLine("Name: {0}", name);
Console.WriteLine("SSN: {0}", ssn);
}
}
class Employee: Person
{
public string id = "ABC567EFG";
public override void GetInfo()
{
// Calling the base class GetInfo method:
base.GetInfo();
Console.WriteLine("Employee ID: {0}", id);
}
}
class TestClass {
public static void Main()
{
Employee E = new Employee();
E.GetInfo();
}
}

38). Difference Between Query String and Session

Querystring	Session
Querystring is client side state management technique.	Session is server side state management technique.
Querystring data is page specific i.e. can be accessed in that page only.	Session data can be accessed throughout the session.
Querystring data is visible to user and can be seen in browser url.	Session data is not visible to user.
Data is not secured and can be altered hence insensitive data is stored in querystring.	Data is secured hence sensitive data such as user information is stored.
Querystring has constraint of Maxlength.	Session does not have such constraint.

39). Difference between Query string and Cookies

cookies is a text file stored on client machine when we surf ant thing on internet by the server automatically we dont have to create it

query string is used to transfer data from 1 page to anothe but this is not safe s it shows in url what data we r sending
pen any site and see url after question mark tht is url

Cookies: - Cookies are little pieces of information that a server stores on a browser. They are of two types
1. Temporary cookie
2. Persistent cookie

Temporary cookie: - They are also known as session cookies. These are volatile in nature. When the browser is shutdown they are erased.

Persistent cookie:- These may be called as permanent cookies. These are especially saved in files. It may remain for a month or year.

Properties of cookies
Some properties of cookie
Name: - represent the name of cookie.
Name value: - represent a collection of key values of cookie
Domain: - represent the domain associated with a specific cookie.
Path: - the path associated with a cookie.
Expires: - expired time of cookie.
Hashkey: - identifies whether the cookie is a cookie dictionary.
Secure: - specifies whether the cookie is to be sent in an encrypted connection or not
Query string is the limited way to pass information to the web server while Transferring from one page to another page. This information is passed in url of the request. see below the code sample

Code Sample

//Retrieving values from query string
String name;
//Retrieving from query string
name = Request.Param["umar"].ToString();

But remember that many browsers impose a limit of 255 characters in query strings. You need to use HTTP-Get method to post a page to server otherwise query string values will not be available.

40). How can we identify that the Page is Post Back?

Page object has an "IsPostBack" property, which can be checked to know that is the page posted back.

41). What is the lifespan for items stored in ViewState?

PThe items stored in ViewState live until the lifetime of the current page expires including the postbacks to the same page

42). What is AutoPostBack?

If you want a control to postback automatically when an event is raised, you need to set the AutoPostBack property of the control to True

43). Why do you use the App_Code folder in ASP.NET?

The App_Code folder is automatically present in the project. It stores the files, such as classes, typed data set, text files, and reports. If this folder is not available in the application, you can add this folder. One of the important features of the App_Code folder is that only one dll is created for the complete folder, irrespective of how many files it contains.

44). In which event of page cycle is the ViewState available?

After the Init() and before the Page_Load().

45). How long the items in ViewState exists?

They exist for the life of the current page.

46). Where the viewstate is stored after the page postback?

ViewState is stored in a hidden field on the page at client side. ViewState is transported to the client and back to the server, and is not stored on the server or any other external source.

47). What are the different Session state management options available in ASP.NET?

In-Process
Out-of-Process.

In-Process stores the session in memory on the web server.

Out-of-Process Session state management stores data in an external server. The external server may be either a SQL Server or a State Server. All objects stored in session are required to be serializable for Out-of-Process state management.

48). What is the difference between web config and machine config?

Web config file is specific to a web application where as machine config is specific to a machine or server. There can be multiple web config files into an application where as we can have only one machine config file on a server.

49). What are the different types of cookies in ASP.NET?

Session Cookie – Resides on the client machine for a single session until the user does not log out.
Persistent Cookie – Resides on a user’s machine for a period specified for its expiry, such as 10 days, one month, and never.

50). What is the difference between ExecuteScalar and ExecuteNonQuery?

ExecuteScalar returns output value where as ExecuteNonQuery does not return any value but the number of rows affected by the query. ExecuteScalar used for fetching a single value and ExecuteNonQuery used to execute Insert and Update statements.

Explain about Partial Class and partual methods

2014-05-26T04:00:00.003-07:00

Introduction

Recently I was researching about partial classes and their real world use. Many of the postings found on Google talked about the concept of partial classes and partial methods, but very few highlighted in what scenarios to use them.

In this article, we will first start with the fundamentals of partial classes and methods and then discuss four real world uses. I have also created a video here where I have discussed about partial classes and shown their real world use.

Fundamentals of partial classes

A partial class allows a single class to be divided into two separate physical files. During compile time, these files get compiled into a single class. For instance, you can see in the below figure we have the customer class divided into two different files “customer1.cs” and “customer2.cs”.

During compilation, these files get compiled into a single class internally. So when you create an object of theCustomer class, you will be able to see methods lying in both the physical files. For instance, you can see the Addmethod belongs to customer1.cs and the Delete method belongs to customer2.cs, but when the Customer object is created, we can see both the Add and Delete methods.

Fundamentals of partial methods

There is one more important concept in partial classes called partial methods. Partial methods helps us to define a method in one physical file and we can implement that method in another physical file, as shown in the below figure.

In the figure, you can see we have defined the Validate method in Customer1.cs and this Validate method is implemented in Customer2.cs. Please note the partial keywords attached to both of these methods.

Use number 1: ASP.NET auto generated code

The biggest use of partial classes is in technologies where there is code generation. The Microsoft team themselves use partial classes in ASP.NET, LINQ, and EF code generation. For instance when we look at ASP.NET, there are two parts: the auto generated code of a page and the code-behind where you write your custom logic.

The custom logic is written in the “.aspx.cs” file while the auto generated logic is in the “.aspx.designer.cs” file, as shown in the below figure.

As a developer, you would like the auto generated code to do its work, i.e., generate code when you drag and drop a button in the ASP.NET designer.

Below is how the auto generated code looks like:

Collapse | Copy Code

public partial class WebForm1 {
        
    /// <summary>
    /// form1 control.
    /// 
    /// <remarks>
    /// Auto-generated field.
    /// To modify move field declaration from designer file to code-behind file.
    /// </remarks>
    protected global::System.Web.UI.HtmlControls.HtmlForm form1;
    
    /// <summary>
    /// Button1 control.
    /// </summary>
    /// <remarks>
    /// Auto-generated field.
    /// To modify move field declaration from designer file to code-behind file.
    /// </remarks>
    protected global::System.Web.UI.WebControls.Button Button1;
        
    /// <summary>
    /// Label1 control.
    /// </summary>
    /// <remarks>
    /// Auto-generated field.
    /// To modify move field declaration from designer file to code-behind file.
    /// </remarks>
    protected global::System.Web.UI.WebControls.Label Label1;
}

At the same time, you would also like to customize the code in some other file in such a way that the auto generation part is not disturbed. For that, ASP.NET provides the “.aspx.cs” file which is a partial class where you can put your own custom logic.

Collapse | Copy Code

public partial class WebForm1 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        // Your custom logic
    }
}

This is only possible when the class is split into two physical files but united via the partial keyword. So if you look at any ASP.NET code-behind class file, it’ll be marked with the word partial.

By using the partial keyword in ASP.NET, the Microsoft team has made VS and developers work side by side thus not fiddling with each other’s code and increasing productivity.

Use number 2: LINQ and Entity Framework

LINQ and EF also use partial classes and methods heavily because of the auto generation nature of these technologies. So when you drag tables in these framework, they create auto generated classes as shown in the below figure.

In the figure, you can see how the auto generated code has partial classes and partial methods.

The partial methods later can be extended to put custom logic. For instance, you can see in the below code that for the above auto-generated class tblCustomer, we have used partial methods to override the OnCustomerCodeChangedevent to ensure that customer code is not more than 8 characters.

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public partial class tblCustomer
{
    partial void OnCustomerCodeChanged()
    {
        if (_CustomerCode.Length > 8)
        {
            throw new Exception("Customer code can not be greater than 8");
        }
    }
}

So by using partial classes and partial methods, LINQ and EF keep auto generating classes and by using partial methods, we can customize the classes with our own logic.

Use number 3: Better maintenance by compacting large classes

The other important use of partial classes is for better maintenance of the project. If you have large classes with lots of methods as shown in the figure, it’s a bit of a pain to maintain those classes.

By using partial classes, you can split them into physical files as shown in the below figure, thus making your project better and easy to maintain.

Use number 4: Multiple people working on the same class

The last and final real world use I see of partial classes is when we want developers to work simultaneously in the same class. I agree this can be a very rare use as there are better options like using a version control software like TFS or Subversion, but in case you want something quick and local, this option is not bad at all.

SSL on IIS 7.0

2014-05-26T03:59:00.002-07:00

SSL enables browsers to communicate with a web-server over a secure channel that prevents eavesdropping, tampering and message forgery. You should always use SSL for login pages where users are entering usernames/passwords, as well as for all other sensitive pages on sites (for example: account pages that show financial or personal information).

Configuring SSL on Windows with previous versions of IIS has been a pain. Figuring out how to install and manage a certificate, and then associate it with a web-site, is something I bet most web developers don't know how to enable.

The good news is that IIS 7.0 makes it radically easier to configure and enable SSL. IIS 7.0 also now has built-in support for creating "Self Signed Certificates" that enable you to easily create test/personal certificates that you can use to quickly SSL enable a site for development or test purposes.

Using IIS 7.0 you can SSL enable an existing web site in under 30 seconds. The below tutorial demonstrates how to-do this.

Step 1: Create a New Web Site

We'll start by creating a new web-site using the new IIS 7.0 admin tool. This admin tool is a complete re-write of the previous IIS admin tool (and was written entirely in managed code using Windows Forms), and provides a more logical organization of web features. It provides a GUI admin experience for all ASP.NET and IIS settings:

To create a new site on the box, right click on the "Web Sites" node in the left hand tree-view pane and choose the "Add Web Site" context menu option. Enter the appropriate details to create a new web-site:

One nice feature of IIS7 on Windows Vista is that you can now have an unlimited number of sites on a box (previous versions of IIS on Windows Client only allowed 1 site). The 10 simultaneous request limitation on Windows Client versions of IIS also no longer exists with IIS 7.0.

Once we've completed the above steps, we will now have a brand new site running on our IIS web-server.

Step 2: Create a new Self Signed Certificate

Before binding SSL rules to our new site, we need to first import and setup a security certificate to use with the SSL binding.

Certificates are managed in IIS 7.0 by clicking the root machine node in the left-hand tree-view explorer, and then selecting the "Server Certificates" icon in the feature pane on the right:

This will then list all certificates registered on the machine, and allow you to optionally import and/or create new ones.

I could optionally go to a certificate authority like Verisign and purchase a certificate to import using this admin UI. Alternatively, I can create a "self-signed certificate" which is a test certificate that I can use during the development and testing of my site. To-do this, click the "Create Self-Signed Certificate" link on the right-hand side of the admin tool:

Enter a name to use for the certificate (for example: "test") and hit ok. IIS7 will then automatically create a new self-signed crypto certificate for you and register it on the machine:

Step 3: Enable HTTPS Bindings for our New Site

To SSL enable the web-site we created earlier, select the web-site node in the left-hand tree-view, and the click the "Bindings" link in its "actions" pane on the right-hand side of the screen:

This will then bring up a dialog that lists all of the binding rules that direct traffic to this site (meaning the host-header/IP address/port combinations for the site):

To enable SSL for the site, we'll want to click the "Add" button. This will bring up an "add binding" dialog that we can use to add HTTPS protocol support. We can select the self-signed certificate we created earlier from the SSL certificate dropdownlist in the dialog, and in doing so indicate that we want to use that certificate when encrypting content over SSL:

Click ok, and we now have SSL enabled for our site:

Step 4: Test out the Site

Add a "default.aspx" page to the site, and then try and hit it with the browser by typing https://localhost/default.aspx (note the usage of "https" instead of "http" to indicate that you want to connect over SSL).

If you are using IE7, you'll likely see this anti-phishing error message kick in

Don't panic if this happens - it is just IE being helpful by suggesting that a self-signed certificate on your local machine looks suspicious. Click the "Continue to this website" link to bypass this security warning and proceed to the site. You'll find that your default.aspx page is now running protected via SSL:

You are all done. :-)

Appendix: A Few Last SSL Notes

A few last SSL related notes:

The IIS 7.0 admin tool has an "SSL Settings" node that you can select for each site, directory or file that allows you to control whether that particular resource (and by default its children) requires an SSL request in order to execute. This is useful for pages like a login.aspx page, where you want to guarantee that users can only enter their credentials when they are posting via an encrypted channel. If you configure the login.aspx page to require SSL, IIS 7.0 will block browsers from accessing it unless they are doing so over SSL.

Within an ASP.NET page or handler, you can programmatically check whether the current request is using SSL by checking the Request.IsSecure property (it will return "true" if the incoming browser request is over SSL).

You can set the "requireSSL" attribute on the <forms> configuration section within web.config files to have ASP.NET's forms-authentication system ensure that forms-authentication cookies are only set and used on SSL enabled pages and URLs. This avoids the risk of a hacker trying to intercept the authentication cookie on a non-SSL secured page, and then trying to use a "replay attack" from a different machine to impersonate a user.

Explain about Constant and ReadOnly and Static

2014-05-26T03:57:00.004-07:00

Constant and ReadOnly keyword are used to make a field constant which value cannot be modified. Static keyword is used to make members static that can be shared by all the class objects. In this article, I am going to explain the difference among these three.

Constant

Constant fields or local variables must be assigned a value at the time of declaration and after that they cannot be modified. By default constant are static, hence you cannot define a constant type as static.


public const int X = 10;

A const field is a compile-time constant. A constant field or local variable can be initialized with a constant expression which must be fully evaluated at compile time.


void Calculate(int Z)
{
 const int X = 10, X1 = 50;
 const int Y = X + X1; //no error, since its evaluated a compile time
 const int Y1 = X + Z; //gives error, since its evaluated at run time
}

You can apply const keyword to built-in value types (byte, short, int, long, char, float, double, decimal, bool), enum, a string literal, or a reference type which can be assigned with a value null.


const MyClass obj1 = null;//no error, since its evaluated a compile time
const MyClass obj2 = new MyClass();//gives error, since its evaluated at run time

Constants can be marked as public, private, protected, internal, or protected internal access modifiers.

Use the const modifier when you sure that the value a field or local variable would not be changed.

ReadOnly

A readonly field can be initialized either at the time of declaration or with in the constructor of same class. Therefore, readonly fields can be used for run-time constants.


class MyClass
{
 readonly int X = 10; // initialized at the time of declaration
 readonly int X1;
 
 public MyClass(int x1)
 {
 X1 = x1; // initialized at run time
 }
}

Explicitly, you can specify a readonly field as static since, like constant by default it is not static. Readonly keyword can be apply to value type and reference type (which initialized by using the new keyword) both. Also, delegate and event could not be readonly.

Use the readonly modifier when you want to make a field constant at run time.

Static

The static keyword is used to specify a static member, which means static members are common to all the objects and they do not tied to a specific object. This keyword can be used with classes, fields, methods, properties, operators, events, and constructors, but it cannot be used with indexers, destructors, or types other than classes.


class MyClass
{
 static int X = 10;
 int Y = 20;
 public static void Show()
 {
 Console.WriteLine(X);
 Console.WriteLine(Y); //error, since you can access only static members
 }
}

Key points about Static keyword

If the static keyword is applied to a class, all the members of the class must be static.
Static methods can only access static members of same class. Static properties are used to get or set the value of static fields of a class.
Static constructor can't be parameterized and public. Static constructor is always a private default constructor which is used to initialize static fields of the class.

-------------------------------------------------------------------------------------------------------

These are very common keywords and are quite confusing. So today we will discuss these keywords and try to understand them.
1. Const: Const is nothing but "constant", a variable of which the value is constant but at compile time. And it's mandatory to assign a value to it. By default a const is static and we cannot change the value of a const variable throughout the entire program.
  
  Here I have created a class named Variables and defined all three variables, so first let's play with const.
  
  Here I tried to de-initialize the const variable, it gaves me an error like "A const field requires a value to be provided". Ok now I initialize a value for this variable and try to change it further in the class.
  
  Here I have created a static constructor, default constructor, parameterized constructor and a Simple Method. I tried to change the value of the const variable everywhere but once I assign the value, I am unable to change it again since when I do it gives me a compile time error as you can see in the snapshot above.
  
  Now let's on to the readonly keyword.
2. Readonly: Readonly is the keyword whose value we can change during runtime or we can assign it at run time but only through the non-static constructor. Not even a method. Let's see:
  
  Here first I try to initialize the value in the static constructor. It gives me an error. Which you can see above.
  Now I try to change the value in a method, see what happened:
  
  Here, it is also giving an error that you can only assign a value either through a variable or a constructor.
  Now try to change the value in the default constructor.
  
  Now in the snapshot above you can see it's built successfully without an error, warning or messages. Let's check if there is a runtime error. OK.
  
  Now here we can see that there is not a runtime error and the value was assigned successfully to the Readonly variable.
  Now one gotcha is, now that you have assigned the value, can you change this value again ???
  Let's try to change the value again.
  
  Here I created a parameterized constructor and created a new object, and passing a value as "Hello Frend'z" and as I built it, it gave me the result "Build Succeeded". Now let's move ahead and check for a runtime error:
  
  See guys. There is no runtime error !! And the value can be changed again and again through a constructor.
  
  Now move ahead to Static Readonly variables.
3. Static ReadOnly: A Static Readonly type variable's value can be assigned at runtime or assigned at compile time and changed at runtime. But this variable's value can only be changed in the static constructor. And cannot be changed further. It can change only once at runtime. Let's understand it practically.
  
  Now in the preceding you can see that I used two variables, one is not assigned and another is assigned, and the static constructor. Now in the static constructor you can see that the unassigned variable is being assigned and the assigned value is being changed. And there is no compile time error. Further I try to again change this variable's value. See what happened:
  
  As you can see in the above, I created Default, Parameterized Constructor and Method and tried to change the value again here. But I am getting a compile time error for all.

Exception Handling in C#.Net

2013-10-15T00:15:00.004-07:00

1. Introduction to Exceptions

An Exception is an object delivered by the Exception class. This Exception class is exposed by the System.Exception namespace. Exceptions are used to avoid system failure in an unexpected manner. Exception handles the failure situation that may arise. All the exceptions in the .NET Framework are derived from the System.Exception class.
To understand exception, we need to know two basic things:

Somebody sees a failure situation that happened and throws an exception by packing the valid information.
Somebody who knows that a failure may happen catches the exception thrown. We call it Exception Handler.

Below is a simple example, which shows what happens when an Exception is not handled:

class ExceptionsEx
{
    //001: Start the Program Execution.
    public void StartProgram()
    {
        Console.WriteLine("Making Call to F1() " );
        F1();
        Console.WriteLine("Successfully returned from F1() " );
    }

    //002: Set of Function that calls each other
    public void F1()
    {
        Console.WriteLine("Making Call to F2() " );
        throw new System.Exception();
        F2();
        Console.WriteLine("Successfully returned from F2() " );
    }
    public void F2()
    {
        Console.WriteLine("Inside F2 " );
    }

    //Client 001: Program Entry
    [STAThread]
    static void Main(string[] args)
    {
        //Create the Object and start the Execution
        ExceptionsEx app = new ExceptionsEx();
        app.StartProgram();
    }
}

In the above code, look at the function F1 that throws an Exception. But, there is no handler to deal with the thrown exception. This situation is called an Un-Handled exception situation. When you execute the code, you get an unhandled exception dialog.
The above dialog is shown in debug mode, so you may get a chance to break the execution to see where the exception is thrown (or) continue ignoring the exception (not advisable).
In release mode, you will get un-handled Exception in the form of Application crash.
So, how do we avoid Un-Handled Exception? Simple, handle it.

2. Handling Exception

To handle the exception, we need to place the code within the try block. When an exception occurs inside the try block, the control looks for the catch block and raises an exception that is handled in the catch block. Below is the simple skeleton for the try and catch block:

try
{
    //Some Code that may expected to raise an exception
}
catch
{
    //Raised exception Handled here
}

The above skeleton handles any exception. But, the main disadvantage is that we don’t know what exception is raised and who raised the exception. Below is the example that handles the Exception raised by the function F1 and avoids the crash:

class ExceptionsEx
{
    //001: Start the Program Execution.
    public void StartProgram()
    {
        Console.WriteLine("Making Call to F1() " );
        try
        {
            F1();
        }
        catch
        {
            Console.WriteLine("Some Exception Occurred. 
  I don't know what Exception it is and where it Occurred. Sorry!");
        }
        Console.WriteLine("Successfully returned from F1() " );
    }

    //002: Set of Function that calls each other
    public void F1()
    {
        Console.WriteLine("Making Call to F2() " );
        throw new System.Exception();
        Console.WriteLine("Successfully returned from F2() " );
    }

    //Client 001: Program Entry
    [STAThread]
    static void Main(string[] args)
    {
        //Create the Object and start the Execution
        ExceptionsEx app = new ExceptionsEx();
        app.StartProgram();
    }
}

3. Exception Bubbling

In the above example, we saw that Exception is handled in the catch block. But, the function call order is simple (Call Stack) that is; StartProgram calls the function F1 and F1 raised exception is handled in the catch block of the StartProgram.
Imagine the situation what happens if there are multiple nested function calls, and exception occurred in the fourth or fifth nested call. Look at the picture below:

F1(): Calls F2 within the try block and handles the exception in catch block
F2(): Makes a call to the function F3. But it neither wraps the call for F3 in the try block nor has the exception handler
F3(): Raises an Exception

Note, when the exception is thrown by the function F3, even though the caller is F2, as there is no catch handler, the execution comes out of F2 and enters the catch block of F1. Travelling back from F3->F2->F1 is known as Stack Unwind. And exception occurred in F3 is handled in F1 even when there is no handler at F2 is known as Exception Bubbling.
Below is the example that demonstrates the Exception Bubbling:

using System;

namespace ExceptionHandling
{
    class ExceptionsEx
    {
        //001: Start the Program Execution.
        public void StartProgram()
        {
            Console.WriteLine("Making Call to F1() " );
            try
            {
                F1();
            }
            catch
            {
                Console.WriteLine("Some Exception Occurred. 
  I don't know what Exception it is and where it Occurred. Sorry!");
            }
            Console.WriteLine("Successfully returned from F1() " );
        }

        //002: Set of Function that calls each other
        public void F1()
        {
            Console.WriteLine("Making Call to F2() " );
            F2();
            Console.WriteLine("Successfully returned from F2() " );
        }
        public void F2()
        {
            Console.WriteLine("Making Call to F2() " );
            F3();
            Console.WriteLine("Successfully returned from F2() " );
        }
        public void F3()
        {
            Console.WriteLine("Inside F3 " );
            throw new System.Exception();
        }

        //Client 001: Program Entry
        [STAThread]
        static void Main(string[] args)
        {
            //Create the Object and start the Execution
            ExceptionsEx app = new ExceptionsEx();
            app.StartProgram();
        }
    }
}

4. The Importance of Finally Block

In the above example, we saw that when an exception occurs, we directly jump back on the call stack and travel back searching for the catch handler. What about the piece of code that comes next to the exception raising code? If we do releasing resource and releasing the heap memory in the next couple of statements, that will not get reached. Right?
Finally block is the solution for this. Now look at the improved exception-handling skeleton below:

try
{
}
catch
{
}
finally
{
}

Whatever happens inside the try block, it is guaranteed that finally block gets executed. Hence, all resource releases should be in the finally block. Have a look at the below picture:
Exception raised at function F3 is handled in the function F2. Look at the try block, I marked two blocks of code before exception and code after exception. It is obvious that when an exception raised, the set of code inside the code after exception is never executed. If resources are allocated in code before exception and the allocated resources are released in code after exception, we do have a resource leak for each exception occurred. Also, think about business logic that needs to revert back apart from the resource leak. This is why finally block is introduced.
Whether an Exception occurs or not, the code inside finally block always gets executed. So you can keep all the cleaning code inside the finally block. The attached sample solution explains the above situation. Put a break point in the very first statement of the function public void StartProgram() and examine the situation explained above. Note, the usage of try block with only finally and without catch in function F2. Think about it.

5. What is Exception Class?

This class is provided by .NET Framework to handle any exception that occurred. The Exception class is the base class for all other Exception class provided by .NET Framework.
The exception object has some important properties. Some of then are given below:

Property	Usage
`Message`	Gives detailed information about the message
`StackTrace`	Gives the function stack to show where `exception` is thrown
`Targetsite`	Shows which method throws the `exception`

In the previous example, we only used the catch block and missed all the above said information. The exception object is thrown by the piece of code, which raises an Exception and the handler code catches that Exception object and makes use of the information packed in it. Consider the below example:

void SomefunctionX()
{
 throw new DivideByZeroException();
}

void SomeFunctionY()
{
 try
 {
  SomefunctionX();
 }
catch (DivideByZeroException Ex)
 {
 //Use the Ex here to get information
 }
}

The example was shown just to understand from where the object that is used in the catch block is coming from. Hope, now you know the exception instance created on the throw statement caught in the catch block and used. Note that, the base class of DivideByZeroException is ArithmaticException, which is derived from the System.Exception. Now the question is, May I use ArithmaticException in the catch block? Yes. Why not? That is the beauty of polymorphism. When you do, always keep in mind that you are moving from more specialized information thrown to the generalized one.

6. Handler for Multiple Exceptions

A code placed in the try block can raise different kinds of exception. It can be say, a Divide by Zero or a Network System Access Denied or a File not exists. How do you handle all the exceptions? The answer is, you can place multiple catch blocks for a try block. When an exception is thrown, type of that exception is examined against each catch block. When a match occurs (even polymorph), the exception enters into the catch block and gets handled.
Let me walk through an example, which will explain the following to you:

Make use of Exception object in the catch block
Using multiple catch blocks for different exceptions
The importance order of the catch blocks

1) Program enters the main function and calls the member function StartProgram after creating the object of type ExceptionsP2.

[STAThread]
public static void Main(string[] args)
{
 ExceptionsP2 start = new ExceptionsP2();
 start.StartProgram();
}

2) The StartProgram function makes a call to Calculate function. And this call is placed in the try block as it is expected that there be some arithmetic exception and possibly a Divide by Zero exception. Two catch blocks are placed for the try block of code. One is DivideByZeroException and other one is System.Exception. Inside each catch block, the exception object caught was used to display the Exception message, and function call stack of where the exception raised. Below is the code:

//001: Function that Handles the Exception
public void StartProgram()
{
 Console.WriteLine("Calling the Function Calculate");
 try
 {
  Calculate();
 }
 catch (DivideByZeroException Ex)
 {
  Console.WriteLine("Divide By Zero. 
   Look at the Call stack for More information");
  Console.WriteLine("Packed Message: " +  Ex.Message );
  Console.WriteLine("Thrown By: " + Ex.TargetSite );
  Console.Write("Call Stack: " + Ex.StackTrace );
 }
 catch (Exception Ex)
 {
  Console.WriteLine("General Exception Occurred");
  Console.WriteLine("Packed Message: " +  Ex.Message );
  Console.Write("Call Stack: " + Ex.StackTrace );
 }
}

3) The calculate is just an intermediate function which makes a call to Divide. Note how the stack rewind and exception bubbling is happening. Below is the function which makes a call to divide, and does not have any Exception handler code:

//002: An intermediate function, just for Demo Purpose
public void Calculate()
{
 Console.WriteLine("Calling Divide Function ");
 Divide();
}

4) The divide function tries to divide a number by zero. The .NET environment detects the situation and raises the exception for us. Note there is no throw statement here. In my previous examples (actually in the previous part), I forced the system to throw an Exception for my demonstration purpose. We usually use the throw statement for Custom defined exceptions. The .NET environment is smart enough to detect the exception at right time and raise it. Below is the code for divide:

//003: The Divide function which actually raises an Exception
public void Divide()
{
 int x = 10;
 int y = 0;
 y = x / y;   
}

7. Closing Notes

The DivideByZeroException thrown in the Divide function is caught by the StartProgram function. Then the exception object is matched against the first catch block. As there is a match, the exception enters that catch block.
What happens if System.Exception catch block is before the DivideByZeroException? We do enter the System.Exception catch block even though a more perfect match exists. Because, the exception caught is matched from top to bottom. As the System.Exception is on the top (that is; Before DivideByZero) and the caught Exception DivideByZeroException is polymorphically a System.Exception the execution control just enters the System.Exception catch block.
So always keep in mind to place more specific catch statement first and move down with more Generalized Exceptions. Look at the code below how a smart developer placed his catch block based on what his Team Lead told.
Lead: “The code block may raise a DivideByZeroException or Any ArithmeticException. It is possible to have FileNotFound Exception also. These are the possibilities of Exception I am seeing when I am reviewing your code. But, for safety, try to handle all exceptions in the world and it is OK if it is not more specific”.
That's all, the Lead went to a meeting.
Forget what meeting he is going for, see how the developer placed his catch block:

try
{
 // The set of code and function here
 // reviewed by an Experienced lead.
}
catch (System.FileNotFoundException Ex)
{
 //File Not Found Exception is Different from Divide by zero.
 //Look at the Inheritance hierarchy in MSDN for FileNotFoundException
 //and DivideByZeroException.
 //So I don't care Which one First, FileNotFond or DivideByZero
}
catch( System.DivideByZeroException Ex) 
{
 //Divide by Zero Exception. Need More Specialized care
}
catch (System.ArithmeticException Ex)
{
 // For any ArithmaticException except DivideByZero. Because I already handled it 
 // before this catch statement
}
catch(System.Exception Ex)
{
 //I am not expecting that this would Occur. As per my Lead
 //I placed it for safe to handle any Exception in the world 
 // That derived from Exception.
}
finally
{
 //Clean-up code
}

Explain about DefaultIfEmpty() in LINQ

2013-10-15T00:10:00.005-07:00

Using Linq DefaultIfEmpty() extension method

By Using DefaultIfEmpty() extension method you can check the sequence for empty and return something for it and do some manipulation on it afterwards.

For example

var numbers = new int[] {1,2,3,4,5,6,7};

Console.WriteLine(numbers.DefaultIfEmpty().Sum());

If the sequence is empty it will return 0 otherwise it will sum and return that.

By Default if you want to return some value other then 0 it will return that as well

Console.WriteLine(numbers.DefaultIfEmpty(100).Sum());

In this case it will return 100 if the sequence is empty.

Explain about ISAPI DLL and ISAPI Filter

2013-10-15T00:10:00.000-07:00

ISAPI (Internet Server Application Program Interface) is a set of Windows program calls that let you write a Web server application that will run faster than a common gateway interface (CGI) application. A disadvantage of a CGI application (or "executable file," as it is sometimes called) is that each time it is run, it runs as a separate process with its own address space, resulting in extra instructions that have to be performed, especially if many instances of it are running on behalf of users. Using ISAPI, you create a dynamic link library (DLL) application file that can run as part of the Hypertext Transport Protocol (HTTP) application's process and address space. The DLL files are loaded into the computer when HTTP is started and remain there as long as they are needed; they don't have to be located and read into storage as frequently as a CGI application.
A special kind of ISAPI DLL is called an ISAPI filter, which can be designated to receive control for every HTTP request. You can create an ISAPI filter for encryption or decryption, for logging, for request screening, or for other purposes.

Introduction

Unless you have been a caveman, you have seen a number of web sites that whenever is browsed, the navigation ends up to a DLL file residing in a scripting directory of that dominium! Something like the following pseudo URL:

http://www.mydomain.com/script/example.dll?ID=p05874&Tx=870250AZT6

What does this DLL suppose to do and what does it have to do with today's paper?
These DLLs are created using the Internet Server API, or ISAPI for short. ISAPI is developed to provide a benefit or two, over the shortcomings of Common Gateway Interface, CGI. Although we surprisingly experience new web sites developed exclusively by CGI scripts nowadays, however, ISAPI DLLs have got something to offer that CGI could never bring us this way or that way.
I am going to start off this paper by describing the underlying details that any ISAPI programmer has to know, to be able to develop a better ISAPI extension. From then on, I will go through a development of a useful ISAPI extension step by step. The extension is supposed to validate a given credit card. Yeah! This is also my answer to those people who asked me the algorithm involved validating a credit card over and over again. Gotta go!

What is ISAPI?

Internet Server Application Programming Interface (ISAPI), is an API developed to provide the application developers with a powerful way to extend the functionality of Internet Information Server (IIS). Although ISAPI extensions by no means are limited to IIS, they are extensively used in conjunction with MS-IIS.

CGI vs. ISAPI

Developing a CGI program involves creating an EXE with C, C++, and/or Perl programming languages. This EXE file will be executed and terminated for every request received, causing an excessive memory usage, whenever users hit the same page over and over again!
This excessive memory usage that could bring the server completely down, has been solved under ISAPI extensions. An ISAPI extension is a regular DLL file that exposes 3 special functions that is called by the calling process (i.e., IIS) and therefore, will be loaded to memory once, no matter how many clients are going to use it at the same time. (It would be a good idea if you could take a look at a reference, to see how memory management is done under Windows 2000. The Visual C++ 6.0 Bible, Chapter 18, The Memory Management, describes it well!)

ISAPI fundamentals

Since the ISAPI extension and the calling process (IIS) live at the same address space, they could contact each other, directly. This means a great potential to bring the whole IIS down, and in some cases, the entire web server! Take a look at the following figure:

You see whatever problem your extension encounters, it could affect the entire web server process, if it's not handled properly. As illustrated above, communicating between the extension and IIS is done via a pointer to a structure of type ECB, or Extension Control Block that is declared as follows:

typedef struct _EXTENSION_CONTROL_BLOCK
{
   DWORD     cbSize;                 // size of this struct.
   DWORD     dwVersion;              // version info of this spec
   HCONN     ConnID;                 // Context number not to be modified!
   DWORD     dwHttpStatusCode;       // HTTP Status code
   CHAR      lpszLogData[HSE_LOG_BUFFER_LEN];// null terminated log info

   LPSTR     lpszMethod;             // REQUEST_METHOD
   LPSTR     lpszQueryString;        // QUERY_STRING
   LPSTR     lpszPathInfo;           // PATH_INFO
   LPSTR     lpszPathTranslated;     // PATH_TRANSLATED

   DWORD     cbTotalBytes;           // Total bytes indicated from client
   DWORD     cbAvailable;            // Available number of bytes
   LPBYTE    lpbData;                // pointer to cbAvailable bytes

   LPSTR     lpszContentType;        // Content type of client data

   BOOL (WINAPI * GetServerVariable) (HCONN hConn,
   LPSTR      lpszVariableName,
   LPVOID     lpvBuffer,
   LPDWORD    lpdwSize );

   BOOL (WINAPI * WriteClient)  (HCONN ConnID,
   LPVOID     Buffer,
   LPDWORD    lpdwBytes,
   DWORD      dwReserved );

   BOOL (WINAPI * ReadClient)  (HCONN ConnID,
   LPVOID     lpvBuffer,
   LPDWORD    lpdwSize );

   BOOL (WINAPI * ServerSupportFunction)( HCONN hConn,
   DWORD      dwHSERequest,
   LPVOID     lpvBuffer,
   LPDWORD    lpdwSize,
   LPDWORD    lpdwDataType ); 

}EXTENSION_CONTROL_BLOCK, *LPEXTENSION_CONTROL_BLOCK;

Whatever information either the calling process or the extension wants to pass to the other, is done through this control block. We will shortly have a look at this ECB structure. For now, let's see how IIS works in conjunction with your extension, to serve the visitor of your web site.
Whenever an extension is accessed (e.g., http://www.mydomain.com/script/example.dll?ID=p05874 & Tx=870250AZT6), IIS checks to see whether the example.dll is loaded into memory. If it is not, then it initiates the loading process. Once the DLL is loaded into memory, a worker thread starts running to manage our extension, and thereafter the entry point (DLLMain function) is called. When the DLLMain finishes, the server makes a call to GetExtensionVersion function to perform two tasks:

Exchange version information
Get a short text description of the extension

The server then calls the HttpExtensionProc function passing a copy of the ECB's pointer to start the actual ISAPI extension. This is the function that makes writing data back to the client, possible! We will examine this, shortly.
The third and the last entry point in an ISAPI extension DLL is the TerminateExtension function that is called whenever the extension is going to be unloaded from the memory. All the cleanup code can be done in this function.
In brief, an ISAPI extension is a regular DLL that exposes 3 functions to interact with the server:

GetExtensionVersion
HttpExtensionProc
TerminateExtension (optional)

Having this information in hand, let's start with the DLLMain, the entry point of any DLL!

DLLMain, the entry point

As indicated by Microsoft, "the DllMain function is an optional entry point into a dynamic-link library (DLL). If the function is used, it is called by the system when processes and threads are initialized and terminated, or upon calls to the LoadLibrary and FreeLibrary functions", that is prototyped as follows:

BOOL APIENTRY DllMain(HANDLE hModule, DWORD dwCallReason, 
                                            LPVOID lpReserved);

If you provide your extension with this function, it will be called upon the initialization and the termination process of your extension. The state is indicated by the dwCallReason parameter that could be one the following predefined values:

DLL_PROCESS_ATTACHED
DLL_THREAD_ATTACH
DLL_THREAD_DETACH
DLL_PROCESS_DETACH

Describing each of these parameters in detail is beyond the scope of this paper, so I simply refer you to Microsoft's Developer Network to read more about this function.
Anyhow, we could save the hModule parameter for later use in our extension (if this suites us) and simply return TRUE from this function. We usually do not have anything to do in this function, while developing an extension!

GetExtensionVersion, the actual entry point

This function is actually the first entry point that is called by IIS to determine the information about the extension. To understand this better, let's have a look at it's prototype:

BOOL WINAPI GetExtensionVersion(HSE_VERSION_INFO *pVer);

Upon the activation of this function, we are supposed to fill out the extension information within the pVer parameter passed to the function. This pointer is of type HSE_VERSION_INFO that is declared as follows:

typedef struct _HSE_VERSION_INFO
{
   DWORD dwExtensionVersion;
   CHAR lpszExtensionDesc[HSE_MAX_EXT_DLL_NAME_LEN];
}HSE_VERSION_INFO, *LPHSE_VERSION_INFO;

where dwExtensionVersion is the extension version and lpszExtensionDescription is the description of the extension. If we return TRUE from this function, we notify IIS that our extension is ready to be used. Otherwise, IIS will not use the extension.

HttpExtensionProc, the main entry point

The amazing part of any ISAPI extension starts when the extension procedure (HttpExtensionProc) is called. As far as you could remember, this is the procedure that makes writing data back to the client possible! To see how this happens, lets start by having a look at the prototype of HttpExtensionProc:

DWORD WINAPI HttpExtensionProc(EXTENSION_CONTROL_BLOCK *pECB);

where pECB is a pointer to an extension control block, that makes the intercommunication between the server and the extension possible. You decide what the web page should contain and how to present it to the user in this entry point. But how?
Do you recall the members of the ECB's structure? ECB contains a method, prototyped as follows:

BOOL WriteClient(HCONN ConnID, LPVOID Buffer, LPDWORD lpdwBytes, 
                                                        DWORD dwSync);

Using this member function, you can send the data present in the given Buffer to the client that is identified by its ConnID, the one that made the request. For example, to send A BIG RED ROSE to a client, you could simply make the following calls:

char szBigRedRos[] = 
  "<font color='#FF0000' size='3'><b>A BIG RED ROSE</b></font>";
DWORD dwSize = strlen(szBigRedRos);
pECB->WriteClient(pECB->ConnID, szBigRedRose, dwSize, 0);

ISAPI filters are DLL files that can be used to modify and enhance the functionality provided by IIS. ISAPI filters always run on an IIS server, filtering every request until they find one they need to process. The ability to examine and modify both incoming and outgoing streams of data makes ISAPI filters powerful and flexible.
Filters are registered at either the site level or the global level (that is, global filters apply to all sites on the IIS server), and are initialized when the worker process is started. A filter listens to all requests to the site on which it is installed.
Both ISAPI filters and ISAPI extensions can only be developed using C/C++. Visual Studio comes with wizards that make ISAPI development fast and easy.

Possible Uses for ISAPI Filters

ISAPI filters can be registered with IIS to modify the behavior of a server. For example, filters can perform the following tasks:

Change request data (URLs or headers) sent by the client
Control which physical file gets mapped to the URL
Control the user name and password used with anonymous or basic authentication
Modify or analyze a request after authentication is complete
Modify a response going back to the client
Run custom processing on "access denied" responses
Run processing when a request is complete
Run processing when a connection with the client is closed
Perform special logging or traffic analysis.
Perform custom authentication.
Handle encryption and compression.

Note:
ISAPI filter DLLs cannot be requested explicitly, like ISAPI extensions can.

ISAPI Filter Processing Sequence

Every ISAPI filter is contained in a separate DLL that must export two entry-point functions, GetFilterVersionand HttpFilterProc, and optionally export the TerminateFilter function. The metabase property, FilterLoadOrder, contains a list of all filters that IIS loads when the Web service is started.

The following steps outline the interaction between ISAPI filters and IIS:

When IIS initially loads an ISAPI filter, it also creates and partially populates an HTTP_FILTER_VERSION structure. It then calls the filter's GetFilterVersion function, passing a pointer to the new structure as a parameter.
The ISAPI filter populates the HTTP_FILTER_VERSION structure with version information and descriptive information. More importantly, the filter also uses HTTP_FILTER_VERSION to specify which event notifications it should receive, and to declare the general priority level for the filter. In addition, the filter also indicates whether it is interested in events from secure ports only, unsecure ports only, or both.
Each HTTP transaction between IIS and a client browser triggers several distinct events. Every time an event occurs for which an ISAPI filter is registered, IIS calls the filter's HttpFilterProc entry-point function.
If more than one ISAPI filter is registered for a given event, IIS notifies the filters that the event occurred. The filters, which are marked as high, medium, or low priority, are notified according to priority in descending order. If more than one ISAPI filter is declared the same general priority level, IIS uses the order in which the filters appear in the FilterLoadOrder property to resolve the tie.
The ISAPI filter uses the notification type information, passed by IIS as a parameter to HttpFilterProc, to determine which particular data structure is pointed to by the other HttpFilterProc parameter, pvNotification. The ISAPI filter then uses the data contained in that data structure, as well as in the context structure HTTP_FILTER_CONTEXT, to perform any custom processing.
Once processing is complete, the filter returns one of the SF_STATUS status codes to IIS, and IIS continues processing the HTTP request or response until another event occurs for which ISAPI filters are registered.
When the Web service is stopped or unloaded, IIS calls TerminateFilter in all ISAPI filters as part of its shutdown sequence, for any filters that implemented and exported the function. TerminateFilter is typically used to perform cleanup and de-allocation of allocated resources.

GetFilterVersion is called exactly once, when the ISAPI filter is initially loaded. Any per-connection initializations the developer wants to perform must be managed internally within the context of the HttpFilterProc function call.

Explain about IEnumerable Interface and yield Keyword

2013-10-08T02:04:00.005-07:00

Introduction

In this article we will discuss about the IEnumerable interface. We will discuss how

IEnumerable

interface facilitate the use of foreach statement to iterate through a set of data. We will then look how to implement our own collections that implement IEnumerable interface. The use of yield keyword and Enumerating generic collections will also be discussed in this article.

Background

Whenever we work with collection of objects, we might find ourselves in need to iterate the collection. The best way to iterate through a collection is by implementing the Iterator pattern. (refer: Understanding and Implementing the Iterator Pattern in C# and C++[^]). C# provides a very clean construct of foreach statement to iterate in a read only manner over a collection.
C# also provides us the possibility of using the same foreach construct and all the enumeration techniques on our custom collection objects by implementing the IEnumerable interface. So let us see how we can implement IEnumerable interface with our custom collection classes.

Using the code

Enumerating the Collection classes

Before starting the discussion let us see how we can use the Built-in classes and iterate over them. Lets start by looking into the ArrayList class that implements IEnumerable and see how we can have read only iteration over that using foreach statement.

// Let us first see how we can enumerate an object implementing IEnumerable
ArrayList list = new ArrayList();

list.Add("1");
list.Add(2);
list.Add("3");
list.Add('4');

foreach (object s in list)
{
    Console.WriteLine(s);
}

Enumerating the Generic Collection classes

The Arraylist class is a generalized class that let us keep a collection. We can also have a generic class in which we can provide the type along with the data. Iterating over generic collection classes is also possible because they implement IEnumerable<T> interface. Lets see how we can enumerate over a generic collection.

// Let us first see how we can enumerate an object implementing IEnumerable<T>
List<string> listOfStrings = new List<string>();

listOfStrings.Add("one");
listOfStrings.Add("two");
listOfStrings.Add("three");
listOfStrings.Add("four");

foreach (string s in listOfStrings)
{
    Console.WriteLine(s);
}

Now our objective is to have our own custom collection class and a generic collection class that should implement the IEnumerable and IEnumerable<T> interface respectively to provide the possibility of enumerating over them.

Understanding the yield keyword

Before jumping into the Implementation of these classes, we need to understand a very important keyword yield which actually facilitate the enumeration over collection. yield statement is used while returning a value from a function.
A normal method call like the one shown below will return only the first value no matter how many times it is called.

static int SimpleReturn()
{
    return 1;
    return 2;
    return 3;
}

static void Main(string[] args)
{
    // Lets see how simeple return works
    Console.WriteLine(SimpleReturn());
    Console.WriteLine(SimpleReturn());
    Console.WriteLine(SimpleReturn());
    Console.WriteLine(SimpleReturn());
}

The reason for this is that the normal return statement does not preserve the state of the function while returning. i.e. every call to this function is a new call and it will return the first value only.
Where as if I replace the return keyword by yield return then the function will become capable of saving its state while returning the value. i.e. when the function is called second time, it will continue the processing from where is has returned in the previous call.

static IEnumerable<int> YieldReturn()
{
    yield return 1;
    yield return 2;
    yield return 3;
}
static void Main(string[] args)
{
    // Lets see how yield return works
    foreach (int i in YieldReturn())
    {
        Console.WriteLine(i);
    }
}

When we run the above code it will return 1,2 and then 3. The only catch while using the yield return statement is that the function should return an IEnumerable and should be called from an iteration block i.e. foreach statement.

Implementing IEnumerable in our custom Collection class

Now in our custom collection classes, if we define a function that will iterate over all the elements in the collection and return then using the yield keyword, we will be able to get hold of all the elements in the the collection.
So let us define our own MyArrayList class and implement IEnumerable interface, which will force us to implement the GetEnumerator function. This function will iterate over the collection and do a yield return on all the elements.

class MyArrayList : IEnumerable
{
    object[] m_Items = null;
    int freeIndex = 0;

    public MyArrayList()
    {
        // For the sake of simplicity lets keep them as arrays
        // ideally it should be link list
        m_Items = new object[100];
    }

    public void Add(object item)
    {
        // Let us only worry about adding the item 
        m_Items[freeIndex] = item;
        freeIndex++;
    }

    // IEnumerable Member
    public IEnumerator GetEnumerator()
    {
        foreach (object o in m_Items)
        {
            // Lets check for end of list (its bad code since we used arrays)
            if(o == null)
            {
                break;
            }

            // Return the current element and then on next function call 
            // resume from next element rather than starting all over again;
            yield return o;
        }
    }
}

This class will now let us enumerate all the elements using a foreach stemement.

static void Main(string[] args)
{
    //Let us now go ahead and use our custom MyArrayList with IEnumerable implemented
    MyArrayList myList = new MyArrayList();

    myList.Add("1");
    myList.Add(2);
    myList.Add("3");
    myList.Add('4');

    foreach (object s in myList)
    {
        Console.WriteLine(s);
    }
}

Note: This class is neither complete not a very good implementation. The only purpose of the sample implementation is to demonstrate the implementation of IEnumerable interface.

Implementing IEnumerable<T> in our custom Generic Collection class

Let us now take this approach a little further and define a generic collection class capable of being enumerated. To do this we need to implement IEnumerable<T> interface.

class MyList<T> : IEnumerable<T>
{
    T[] m_Items = null;
    int freeIndex = 0;

    public MyList()
    {
        // For the sake of simplicity lets keep them as arrays
        // ideally it should be link list
        m_Items = new T[100];
    }

    public void Add(T item)
    {
        // Let us only worry about adding the item 
        m_Items[freeIndex] = item;
        freeIndex++;
    }

    #region IEnumerable<T> Members

    public IEnumerator<T> GetEnumerator()
    {
        foreach (T t in m_Items)
        {
            // Lets check for end of list (its bad code since we used arrays)
            if (t == null) // this wont work is T is not a nullable type
            {
                break;
            }

            // Return the current element and then on next function call 
            // resume from next element rather than starting all over again;
            yield return t;
        }
    }

    #endregion

    #region IEnumerable Members

    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    {
        // Lets call the generic version here
        return this.GetEnumerator();
    }

    #endregion
}

This class will now let us enumrate all the elements using a foreach stemement.

static void Main(string[] args)
{
    // Let us first see how we can enumerate an custom MyList<t> class implementing IEnumerable<T>
    MyList<string> myListOfStrings = new MyList<string>();

    myListOfStrings.Add("one");
    myListOfStrings.Add("two");
    myListOfStrings.Add("three");
    myListOfStrings.Add("four");

    foreach (string s in myListOfStrings)
    {
        Console.WriteLine(s);
    }
}
</t>

So now we have a collection class and a generic collectio class that implement IEnumerable and IEnumerable<T> respectively. Althogh These class is neither complete not a very good implementation but they do serve the purpose of the article i.e. to demonstrate the implementation of IEnumerable interface.

Point of interest

What we have tried to do in this article is see how can we implement the IEnumerable and IEnumberable<T> interface. We have looked into the significance of yield keyword. This stuff is known to most experienced C# programmers but the beginners might find it useful. I hope this has been informative.

Explain about CTE and Temp Table and Table Variable

2013-10-08T00:22:00.004-07:00

Temp Table or Table variable or CTE are commonly used for storing data temporarily in SQL Server. In this article, you will learn the differences among these three.

CTE

CTE stands for Common Table expressions. It was introduced with SQL Server 2005. It is a temporary result set and typically it may be a result of complex sub-query. Unlike temporary table its life is limited to the current query. It is defined by using WITH statement. CTE improves readability and ease in maintenance of complex queries and sub-queries. Always begin CTE with semicolon.

A sub query without CTE is given below :


SELECT * FROM (
 SELECT Addr.Address, Emp.Name, Emp.Age From Address Addr
 Inner join Employee Emp on Emp.EID = Addr.EID) Temp
WHERE Temp.Age > 50
ORDER BY Temp.NAME

By using CTE above query can be re-written as follows :


;With CTE1(Address, Name, Age)--Column names for CTE, which are optional
AS
(
SELECT Addr.Address, Emp.Name, Emp.Age from Address Addr
INNER JOIN EMP Emp ON Emp.EID = Addr.EID
)
SELECT * FROM CTE1 --Using CTE 
WHERE CTE1.Age > 50
ORDER BY CTE1.NAME

When to use CTE

This is used to store result of a complex sub query for further use.
This is also used to create a recursive query.

Temporary Tables

In SQL Server, temporary tables are created at run-time and you can do all the operations which you can do on a normal table. These tables are created inside Tempdb database. Based on the scope and behavior temporary tables are of two types as given below-

Local Temp Table
Local temp tables are only available to the SQL Server session or connection (means single user) that created the tables. These are automatically deleted when the session that created the tables has been closed. Local temporary table name is stared with single hash ("#") sign.
```
CREATE TABLE #LocalTemp
(
 UserID int,
 Name varchar(50), 
 Address varchar(150)
)
GO
insert into #LocalTemp values ( 1, 'Shailendra','Noida');
GO
Select * from #LocalTemp
```
The scope of Local temp table exist to the current session of current user means to the current query window. If you will close the current query window or open a new query window and will try to find above created temp table, it will give you the error.
Global Temp Table
Global temp tables are available to all SQL Server sessions or connections (means all the user). These can be created by any SQL Server connection user and these are automatically deleted when all the SQL Server connections have been closed. Global temporary table name is stared with double hash ("##") sign.
```
CREATE TABLE ##GlobalTemp
(
 UserID int,
 Name varchar(50), 
 Address varchar(150)
)
GO
insert into ##GlobalTemp values ( 1, 'Shailendra','Noida');
GO
Select * from ##GlobalTemp
 
```
Global temporary tables are visible to all SQL Server connections while Local temporary tables are visible to only current SQL Server connection.

Table Variable

This acts like a variable and exists for a particular batch of query execution. It gets dropped once it comes out of batch. This is also created in the Tempdb database but not the memory. This also allows you to create primary key, identity at the time of Table variable declaration but not non-clustered index.


 GO
 DECLARE @TProduct TABLE
 (
 SNo INT IDENTITY(1,1),
 ProductID INT,
 Qty INT
 ) 
 --Insert data to Table variable @Product 
 INSERT INTO @TProduct(ProductID,Qty)
 SELECT DISTINCT ProductID, Qty FROM ProductsSales ORDER BY ProductID ASC 
 --Select data
 Select * from @TProduct
 
 --Next batch
 GO
 Select * from @TProduct --gives error in next batch

Note

Temp Tables are physically created in the Tempdb database. These tables act as the normal table and also can have constraints, index like normal tables.
CTE is a named temporary result set which is used to manipulate the complex sub-queries data. This exists for the scope of statement. This is created in memory rather than Tempdb database. You cannot create any index on CTE.
Table Variable acts like a variable and exists for a particular batch of query execution. It gets dropped once it comes out of batch. This is also created in the Tempdb database but not the memory.

Explain about COM and Interoperability in DotNet

2013-09-20T01:08:00.002-07:00

Introduction

Component Object Model is a method to facilitate communication between different applications and languages. There are many other ways to structure software components. What makes COM interesting is that it is a widely accepted interoperability standard. In addition, the standard explains the way the memory should be organized for all the objects.
Interfaces are the contract between the client and the server, i.e. an interface is the way in which an object exposes its functionality to the outside world. In COM, an interface is a table of pointers to functions implemented by the object. The table represents the interface, and the functions to which it points are the methods of that interface.

Creating COM components in .NET

Creating COM components in .NET is not that difficult as in C++. The following steps explain the way to create the COM server in C#:

Create a new Class Library project.
Create a new interface, say IManagedInterface, and declare the methods required. Then provide the Guid (this is the IID) for the interface using the GuidAttribute defined in System.Runtime.InteropServices. The Guid can be created using the Guidgen.exe. [Guid("3B515E51-0860-48ae-B49C-05DF356CDF4B")]
Define a class that implements this interface. Again provide the Guid (this is the CLSID) for this class also.
Mark the assembly as ComVisible. For this go to AssemblyInfo.cs file and add the following statement [assembly: ComVisible (true)]. This gives the accessibility of all types within the assembly to COM.
Build the project. This will generate an assembly in the output path. Now register the assembly using regasm.exe (a tool provided with the .NET Framework)- regasm \bin\debug\ComInDotNet.dll \tlb:ComInDotNet.tlb This will create a TLB file after registration.
Alternatively this can be done in the Project properties -> Build -> check the Register for COM interop.

The COM server is ready. Now a client has to be created. It can be in any language. If the client is .NET, just add the above created COM assembly as reference and use it.

The following steps explain the method to create an unmanaged client. Here the client is in VC++ 6.0.

Create an MFC AppWizard EXE using the wizard in MSDEV 6.0.
Import the COM server (TLB file generated by regasm.exe) using the #import directive. #import “ComInDotNet.tlb” no_namespace named_guids raw_interfaces_only.
Now the COM library should be loaded using the CoInitialize and component can be created using CoCreateInstance.
Next the methods defined in the COM Server can be invoked. pInterface->Execute(“blah blah blah”);
What is COM?
Microsoft COM (Component Object Model) technology in the Microsoft Windows-family of Operating Systems enables software components to communicate. COM is used by developers to create re-usable software components, link components together to build applications, and take advantage of Windows services. COM objects can be created with a variety of programming languages. Object-oriented languages, such as C++, provide programming mechanisms that simplify the implementation of COM objects. The family of COM technologies includes COM+, Distributed COM (DCOM) and ActiveX® Controls.

Microsoft provides COM interfaces for many Windows application programming interfaces such as Direct Show, Media Foundation, Packaging API, Windows Animation Manager, Windows Portable Devices, and Microsoft Active Directory (AD).

COM is used in applications such as the Microsoft Office Family of products. For example COM OLE technology allows Word documents to dynamically link to data in Excel spreadsheets and COM Automation allows users to build scripts in their applications to perform repetitive tasks or control one application from another.
What's new in .NET Framework 3.5 SP1?
SP1 advances the art of application development
The new ADO.NET Entity Framework feature in SP1 offers developers a model-based paradigm and a rich, standards-based framework for creating data-oriented applications shared across multiple applications and platforms. The separation of presentation, data, and business logic used in concert with a single data model will enable developers to spend less time writing plumbing code and more time refining business logic.

SP1 makes data-driven programming easier
SP1 offers developers support for ASP.NET Dynamic Data, which provides a rich scaffolding framework that enables rapid data-driven development. Since ASP.NET takes care of creating the presentation layer, a fully functional Website is output and ready for customization without the developer writing a single line of code. Further, with ADO.NET Data Services, Web developers can create RESTful Web 2.0-style applications that have better server scalability and improved caching support.

SP1 is the fastest and easiest way to deploy Windows applications
With the .NET Framework Client Profile, a small subset of the Framework that powers client applications, developers can offer their end users a dramatically streamlined and rapid application download experience. In addition, improvements in SP1 result in dramatic reductions in cold start times, allowing developers to serve a broader set of customers with varying hardware profiles
Summary
This paper provides the technical overview of .NET and COM interoperability. It describes how .NET components can communicate with existing COM components without migrating those COM components into .NET components, thus helping the migration cost and business systems. This paper also provides an overview of marshalling. The intended audience is a development team that wishes to interact with COM and .NET applications. (This paper assumes that the reader has the fundamental knowledge of COM and .NET)

Introduction
From the time Microsoft engineers started working on the ideas behind COM in 1998, COM went through quite an evolution. Once .NET was released everything was about the CLR. Those business systems made lot of investments on those COM developments and they may not be willing to invest more money to build their components into .NET. Also this will make a severe impact in productivity.
Fortunately, switching from COM to .NET involves no such radical loss of productivity. The concept of providing bridge between .NET and COM components is .NET-COM interoperability. Microsoft .NET Framework provides system, tools, and strategies that enable strong integration with past technologies and allow legacy code to be integrated with new .NET components. It provides a bridge between the .NET and COM and vice versa.
There are two key concepts that make it much easier to move from COM development to .NET development, without any loss of code base or productivity.
Interaction with COM components from .NET
Interaction with .NET components from COM

Before going further, this paper will describe about the basic communication fundamentals of COM and .NET components.

Communication between Object and Client

COM is a binary reusable object which exposes its functionality to other components. When a client object asks for instances of server object, the server instantiates those objects and handout references to the client. So, a COM component can act as a binary contract between caller and callee. This binary contract is defined in a document known as Type library. The Type library describes to a potential client the services available from a particular server. Each COM components will expose a set of interfaces through which the communication between COM components will occurs.
The following diagram shows the communication between a client and a COM object.

Fig.1 Communication between client and a COM object
In the above figure the IUnknown and IDispatch are the interfaces and QueryInterface, AddRef, Release, etc., are the methods exposed by those interfaces.
The communication between the .NET objects occurs through Objects, there are no such interfaces for communication. So, in .NET component, there is no type libraries, instead they deal with assemblies. Assembly is a collection of types and resources that are built to work together and form a logical unit of functionality. All the information related to the assembly will be held in assembly metadata. Unlike the communication between COM components, the communication between .NET components is Object based.

Calling COM components from .NET Client

Generally COM components will expose interfaces to communicate with other objects. A .NET client cannot directly communicate with a COM component because the interfaces exposed by a COM component may not be read by the .NET application. So, to communicate with a COM component, the COM component should be wrapped in such a way that the.NET client application can understand the COM component. This wrapper is known as Runtime Callable Wrapper (RCW).
The .NET SDK provides Runtime Callable Wrapper (RCW) which wraps the COM components and exposes it into to the .NET client application.

Fig.2 calling a COM component from .NET client
To communicate with a COM component, there should be Runtime Callable Wrapper (RCW). RCW can be generated by using VS.NET or by the use of TlbImp.exe utility. Both the ways will read the type library and uses System.Runtime.InteropServices.TypeLibConverter class to generate the RCW. This class reads the type library and converts those descriptions into a wrapper (RCW). After generating the RCW, the .NET client should import its namespace. Now the client application can call the RCW object as native calls.
When a client calls a function, the call is transferred to the RCW. The RCW internally calls the native COM function coCreateInstance there by creating the COM object that it wraps. The RCW converts each call to the COM calling convention. Once the object has been created successfully, the .NET client application can access the COM objects as like native object calls.

Calling .NET components from COM Client

When a COM client requests a server, first it searches in the registry entry and then the communication starts. Calling a .NET component from a COM component is not a trivial exercise. The .NET objects communicate through Objects. But the Object based communication may not be recognized by the COM clients. So, to communicate with the .NET component from the COM component, the .NET component should be wrapped in such a way that the COM client can identify this .NET component. This wrapper is known as COM Callable Wrapper (CCW). The COM Callable Wrapper (CCW) will be used to wrap the .NET components and used to interact with the COM clients.
CCW will be created by the .NET utility RegAsm.exe. This reads metadata of the .NET component and generates the CCW. This tool will make a registry entry for the .NET components.

Fig.3 calling a .NET component from COM client
Generally COM client instantiates objects through its native method coCreateInstance. While interacting with .NET objects, the COM client creates .NET objects by coCreateInstance through CCW.
Internally, when coCreateInstance is called, the call will redirect to the registry entry and the registry will redirect the call to the registered server, mscoree.dll. This mscoree.dll will inspect the requested CLSID and reads the registry to find the .NET class and the assembly that contains the class and rolls a CCW on that .NET class.
When a client makes a call to the .NET object, first the call will go to CCW. The CCW converts all the native COM types to their .NET equivalents and also converts the results back from the .NET to COM.

Programming model comparison of .NET-COM interoperability

The following table compares the .NET and COM based component programming models.

.NET	COM
Object based communication	Interface based communication
Garbage Collector to manage memory	Reference count will be used to manage memory
Type Standard objects	Binary Standard objects
Objects are created by normal new operator	Objects are created by `coCreateInstance`
Exceptions will be returned	`HRESULT` will be returned
Object info resides in assembly files	Object info resides in Type library

Before the application starts to communicate, there are some technical constraints associated with this. When an object is transmitted to a receiver which is in a separate machine/process (managed/unmanaged) space, the object may need to undergo a transformation according to the native type to make it suitable for use by the recipient. That is the object will be converted into a recipient readable form. This process of converting an object between types when sending it across contexts is known as marshaling. The next section of the paper will gives an overview of marshalling in .NET.

.NET Marshalling

Thus .NET runtime automatically generates code to translate calls between managed code and unmanaged code. While transferring calls between these two codes, .NET handles the data type conversion also. This technique of automatically binding with the server data type to the client data type is known as marshalling. Marshaling occurs between managed heap and unmanaged heap. For example, Fig.4 shows a call from the .NET client to a COM component. This sample call passes a .NET string from the client. The RCW converts this .NET data type into the COM compatible data type. In this case COM compatible data type is BSTR. Thus the RCW converts the .NET string into COM compatible BSTR. This BSTR will be passed to the object and the required calls will be made. The results will be returned to back to the RCW. The RCW converts this COM compatible result to .NET native data type.

Fig.4 Sample diagram for marshalling
Logically the marshalling can be classified into 2 types.

Interop marshalling
COM marshalling

If a call occurs between managed code and unmanaged code with in the same apartment, Interop marshaler will play the role. It marshals data between managed code and unmanaged code.
In some scenarios COM component may be running in different apartment threads. In those cases i.e., calling between managed code and unmanaged code in different apartments or process, both Interop marshaler and COM marshaler are involved.

Interop marshaler

When the server object is created in the same apartment of client, all data marshaling is handled by Interop marshaling.

Fig.5 Sample diagram for same apartment marshalling

COM marshaler

COM marshaling involved whenever the calls between managed code and unmanaged code are in different apartments. For eg., when a .NET client (with the default apartment settings) communicates with a COM component (whichever developed in VB6.0), the communication occurs through proxy and stub because both the objects will be running in different apartment threads. (The default apartment settings of .NET objects are STA and the components which are developed by VB6.0 are STA). Between these two different apartments COM marshaling will occurs and with in the apartment Interop marshaling will occurs. Fig.6 shows this kind of marshaling.
This kind of different apartment communication will impact the performance. The apartment settings of the managed client can be changed by changing the STAThreadAttribute / MTAThreadAttribute / Thread.ApartmentState property. Both the codes can run in a same apartment, by making the managed code’s thread to STA. (If the COM component is set as MTA, then cross marshaling will occurs.)

Fig.6 Sample diagram for cross apartment marshalling
In the above scenario, the call with in different apartments will occur by COM marshaling and the call between managed and unmanaged code will occur by Interop marshaling.

Conclusion

Thus the communication between .NET applications and COM applications occurs through RCW and CCW.
As you have seen, COM applications can implement .NET types to achieve type compatibility or a .NET type can implement COM interfaces to achieve binary compatibility with related coclasses.
Although the managed clients can interact with the unmanaged objects, the managed client expects that the unmanaged object should act exactly the same as managed object.
When developing against the unmanaged component through COM interoperability, managed code developers will not be able to use some features of .NET like parameterized constructors, static methods, inheritance, etc., migrating an existing component or writing a managed wrapper will make the component easier to use for managed code developers. In some cases, the developer wants to migrate parts of the application to .NET so that application can take advantage of the new features that the .NET Framework offers. For example, ASP .NET provides advanced data binding, browser-dependent user interface generation, and improved configuration and deployment. The designer should evaluate when the value of bringing these new features in to the application outweigh the cost of code migration.