DevHelp

object oriented vs object based programming language

2013-05-06T11:34:00.000+05:30

Object Base Language Not Support Inheritance & Polimorphisum.

Object-Based Programming usually refers to objects without inheritance and without polymorphism, These languages support abstract data types and not classes,which provide inheritance and polymorphism.

however,support both inheritance and polymorphism and they are object-oriented.

Candidate Key Vs Primary Key Vs Alternate key Vs Composite Key Vs Unique Key VsForeign Key

2013-05-06T10:48:00.000+05:30

Candidate Key

A Candidate Key is a set of one or more fields/columns that can identify a record uniquely in a table. There can be multiple Candidate Keys in one table. Each Candidate Key can work as Primary Key.
Example: In Student Table RollNo and EnrollNo are Candidate Keys since these fields can be work as Primary Key.

Primary Key

Primary key is a set of one or more fields/columns of a table that uniquely identify a record in database table. It can not accept null, duplicate values. Only one Candidate Key can be Primary Key.

Alternate key
A Alternate key is a key that can be work as a primary key. Basically it is a candidate key that currently is not primary key.Example: In RollNo and EnrollNo, RollNo becomes Alternate Keys when we define EnrollNo as Primary Key.

Composite/Compound Key

Composite Key is a combination of more than one fields/columns of a table. It can be a Candidate key, Primary key.

Unique Key

Uniquekey is a set of one or more fields/columns of a table that uniquely identify a record in database table. It is like Primary key but it can accept only one null value and it can not have duplicate values.

Foreign Key

Foreign Key is a field in table that is Primary key in another table. It can accept multiple null, duplicate values. Example : We can have a Emp_Id column in the Employee table which is pointing to Emp_Id column in a department table where it a foreign key.

Interview questions of MVC (Part-1)

2013-04-28T12:31:00.001+05:30

Q:What are the 3 main components of an ASP.NET MVC application?
A1. M - Model
2. V - View
3. C - Controller

Q:In which assembly is the MVC framework defined?
A:System.Web.Mvc

Q:Is it possible to combine ASP.NET webforms and ASP.MVC and develop a single
web application?
A:Yes, it is possible to combine ASP.NET webforms and ASP.MVC and develop a single
web application.

Q:What does Model, View and Controller represent in an MVC application?
A:Model: Model represents the application data domain. In short the applications business logic is
contained with in the model.

View: Views represent the user interface, with which the end users interact. In short the all the user
interface logic is contained with in the UI.

Controller: Controller is the component that responds to user actions. Based on the user actions,
the respective controller, work with the model, and selects a view to render that displays the user
interface. The user input logic is contained with in the controller.

Q:What is the greatest advantage of using asp.net mvc over asp.net webforms?
A:It is difficult to unit test UI with webforms, where views in mvc can be very easily unit tested.

Q:Which approach provides better support for test driven development - ASP.NET MVC or
ASP.NET Webforms?
A:ASP.NET MVC

Q:What are the advantages of ASP.NET MVC?
A:1. Extensive support for TDD. With asp.net MVC, views can also be very easily unit tested.
2. Complex applications can be easily managed
3. Seperation of concerns. Different aspects of the application can be divided into Model, View
and Controller.
4. ASP.NET MVC views are light weight, as they donot use viewstate.

Q:Is it possible to unit test an MVC application without running the controllers in an ASP.NET
process?
A:Yes, all the features in an asp.net MVC application are interface based and hence mocking is
much easier.So, we don't have to run the controllers in an ASP.NET process for unit testing.

Q:Is it possible to share a view across multiple controllers?
A:Yes, put the view into the shared folder. This will automatically make the view available across
multiple controllers.

Q:What is the role of a controller in an MVC application?
A:The controller responds to user interactions, with the application, by selecting the action method
to execute and alse selecting the view to render.

Q:Where are the routing rules defined in an asp.net MVC application?
A:In Application_Start event in Global.asax

ViewModel in MVC

2013-04-22T11:10:00.000+05:30

ViewModel is a complex object that may contain multiple entities or objects from different data models or data source.

ViewModel contain fields that are represented in the view (for LabelFor,EditorFor,DisplayFor helpers)
ViewModel can have specific validation rules using data annotations or IDataErrorInfo.
ViewModel can have multiple entities or objects from different data models or data source.

In ViewModel put only those fields/data that you want to display on the view/page.
Since view reperesents the properties of the ViewModel, hence it is easy for rendering and maintenance.
Use a mapper when ViewModel become more complex.

HTTP Handler Vs HTTP Module

2013-04-22T10:58:00.000+05:30

HTTP Handler :
HTTP handlers are the .NET components that implement the System.Web.IHttpHandler interface. Any class that implements the IHttpHandler interface can act as a target for the incoming HTTP requests. HTTP handlers are somewhat similar to ISAPI extensions. One difference between HTTP handlers and ISAPI extensions is that HTTP handlers can be called directly by using their file name in the URL.

HttpHandler is a extension based processor.

HTTP Module :
Http modules are called before and after the http handler executes. Http modules enable developers to participate in, or modify each individual request. Http modules implement the IHttpModule interface, which is located in the System.Web namespace.

HttpModule is event based processor.

Bind vs Eval (Data Binder)

2013-04-09T17:25:00.000+05:30

The data values can be retrieved with the Eval method – they cannot be modified or deleted.

The Bind method on the other hand allows for the data-bound controls to be modified in addition to retrieval, and hence is preferred over Eval method.

Cast and Convert

2013-04-09T17:19:00.000+05:30

1.CAST and CONVERT are two SQL functions used by programmers to convert one data type to another.

2.The CAST function is ANSI standard and is compatible to use in other databases while the CONVERT function is a specific function of the SQL server.

3.Since the CAST function is compatible with other databases, it is also described as portable though it has fewer features compared to the CONVERT function. The CONVERT function, meanwhile, can do some things that the CAST function cannot.

4.The CAST function is used to convert a data type without a specific format. The CONVERT function does converting and formatting data types at the same time.

5.In terms of syntax, both functions have the optional parameter of length. In the CONVERT function, there is an additional parameter called style which specifies the format of the data type after conversion.

6.The CAST function is often used to preserve decimal values and places while converting them into integers. The function can also truncate the decimal value if needed. The CONVERT function cannot perform this task.

Miscellaneous Features of Global Temporary Tables

2013-04-07T20:23:00.000+05:30

• If the TRUNCATE statement is issued against a temporary table, only the session specific data is
truncated. There is no affect on the data of other sessions.
• Data in temporary tables is stored in temp segments in the temp tablespace.
• Data in temporary tables is automatically deleted at the end of the database session, even if it ends
abnormally.
• Indexes can be created on temporary tables. The content of the index and the scope of the index is the
same as the database session.
• Views can be created against temporary tables and combinations of temporary and permanent tables.
• Temporary tables can have triggers associated with them.
• Export and Import utilities can be used to transfer the table definitions, but no data rows are processed.
• Statistics on temporary tables are common to all sessions. Oracle 12c allows session specific statistics.
• There are a number of restrictions related to temporary tables but these are version specific.

Restrictions on Declared Global Temporary Tables

2013-04-07T20:20:00.000+05:30

You cannot use the following features with temporary tables:

• Synonyms, triggers and views on SESSION schema tables (including physical tables and temporary
tables)
• Caching statements that reference SESSION schema tables and views
• Temporary tables cannot be specified in referential constraints and primary keys
• Temporary tables cannot be referenced in a triggered-SQL-statement
• Check constraints on columns
• Generated-column-spec
• Importing into temporary tables

If a statement that performs an insert, update, or delete to the temporary table encounters an error, all the rows of the temporary table are deleted.

The following data types cannot be used with Declared Global Temporary Tables:

• BLOB
• CHAR FOR BIT DATA
• CLOB
• LONG VARCHAR
• LONG VARCHAR FOR BIT DATA
• VARCHAR FOR BIT DATA
• XML

Creation of Global Temporary Tables

2013-04-07T20:18:00.000+05:30

The data in a global temporary table is private, such that data inserted by a session can only be accessed by that session. The session-specific rows in a global temporary table can be preserved for the whole session, or just for the current transaction. The ON COMMIT DELETE ROWS clause indicates that the data should be deleted at the end of the transaction.

CREATE GLOBAL TEMPORARY TABLE temp_tab (
column1 NUMBER,
column2 NUMBER
) ON COMMIT DELETE ROWS;

In contrast, the ON COMMIT PRESERVE ROWS clause indicates that rows should be preserved until the end of the session.

CREATE GLOBAL TEMPORARY TABLE temp_tab (
column1 NUMBER,
column2 NUMBER
) ON COMMIT PRESERVE ROWS;

Unlike permanent tables, temporary tables and their indexes do not automatically allocate a segment when they are created. Instead, segments are allocated when the first INSERT (or CREATE TABLE AS SELECT) is performed. Therefore, if a SELECT, UPDATE, or DELETE is performed before the first INSERT, then the table appears to be empty.

DDL operations (except TRUNCATE) are allowed on an existing temporary table only if no session is currently bound to that temporary table.

If you rollback a transaction, the data you entered is lost, although the table definition persists.
A transaction-specific temporary table allows only one transaction at a time. If there are several autonomous transactions in a single transaction scope, each autonomous transaction can use the table only as soon as the previous one commits.

Because the data in a temporary table is, by definition, temporary, backup and recovery of temporary table data is not available in the event of a system failure. To prepare for such a failure, you should develop alternative methods for preserving temporary table data.

Global Temporary Tables - Oracle

2013-04-07T20:15:00.002+05:30

Applications often use some form of temporary data store for processes that are too complicated to complete in a single pass. Often, these temporary stores are defined as database tables or PL/SQL tables. In Oracle 8i, the maintenance and management of temporary tables can be delegated to the server by using Global Temporary Tables.
These tables do not reside in the system catalogs and are not persistent. Temporary tables exist only during the connection that declared them and cannot be referenced outside of that connection. When the connection closes, the rows of the table are deleted, and the in-memory description of the temporary table is dropped.

Temporary tables are useful when:

• The table structure is not known before using an application.

• Other users do not need the same table structure.

• Data in the temporary table is needed while using the application.

• The table can be declared and dropped without holding the locks on the system catalog.

Syntax

DECLARE GLOBAL TEMPORARY TABLE table-Name

{ column-definition [ , column-definition ] * }

[ ON COMMIT {DELETE | PRESERVE} ROWS ]

NOT LOGGED [ON ROLLBACK DELETE ROWS]

table-Name

Names the temporary table. If a schema-Name other than SESSION is specified, an error will occur (SQLSTATE 428EK). If the schema-Name is not specified, SESSION is assigned. Multiple connections can define declared global temporary tables with the same name because each connection has its own unique table descriptor for it.

Using SESSION as the schema name of a physical table will not cause an error, but is discouraged. The SESSION schema name should be reserved for the temporary table schema.

column-definition

See column-definition for CREATE TABLE for more information on column-definition. DECLARE GLOBAL TEMPORARY TABLE does not allow generated-column-spec in the column-definition.

Data type

Supported data types are:

• BIGINT

• CHAR

• DATE

• DECIMAL

• DOUBLE

• DOUBLE PRECISION

• FLOAT

• INTEGER

• NUMERIC

• REAL

• SMALLINT

• TIME

• TIMESTAMP

• VARCHAR

ON COMMIT

Specifies the action taken on the global temporary table when a COMMIT operation is performed.

DELETE ROWS

All rows of the table will be deleted if no hold-able cursor is open on the table. This is the default value for ON COMMIT. If you specify ON ROLLBACK DELETE ROWS, this will delete all the rows in the table only if the temporary table was used. ON COMMIT DELETE ROWS will delete the rows in the table even if the table was not used (if the table does not have hold-able cursors open on it).

PRESERVE ROWS

The rows of the table will be preserved.

NOT LOGGED

Specifies the action taken on the global temporary table when a rollback operation is performed. When a ROLLBACK (or ROLLBACK TO SAVEPOINT) operation is performed, if the table was created in the unit of work (or savepoint), the table will be dropped. If the table was dropped in the unit of work (or savepoint), the table will be restored with no rows.

ON ROLLBACK DELETE ROWS

This is the default value for NOT LOGGED. NOT LOGGED [ON ROLLBACK DELETE ROWS ]] specifies the action that is to be taken on the global temporary table when a ROLLBACK or (ROLLBACK TO SAVEPOINT) operation is performed. If the table data has been changed, all the rows will be deleted.

nth highest salary in sql server

2013-04-05T11:27:00.000+05:30

SELECT TOP 1 salary
FROM (
SELECT DISTINCT TOP n salary
FROM employee
ORDER BY salary DESC) a
ORDER BY salary

Access Modifier in .Net

2013-04-03T11:09:00.001+05:30

Visual Basic Modifier	C# Modifier	Definition
Public (Visual Basic)	public	The type or member can be accessed by any other code in the same assembly or another assembly that references it.
Private (Visual Basic)	private	The type or member can only be accessed by code in the same class.
Protected (Visual Basic)	protected	The type or member can only be accessed by code in the same class or in a derived class.
Friend (Visual Basic)	internal	The type or member can be accessed by any code in the same assembly, but not from another assembly.
Protected Friend	protected internal	The type or member can be accessed by any code in the same assembly, or by any derived class in another assembly.

Read tnsnames.ora in VB.NET

2013-04-02T14:39:00.003+05:30

Below are the code for read tnsname.ora file(tns name) in vb.net. Through below functions you can get the information of the tns.

//Declare namespace
Imports System
Imports System.Collections.Generic
Imports System.Text.RegularExpressions
Imports System.IO

Public Class ReadTNS
    //Function for Load TNS Name
    Public Function LoadTNSNames() As List(Of String)
        Dim DBNamesCollection As New List(Of String)()
        Dim regPattern As String = "[\n][\s]*[^\(][a-zA-Z0-9_.]+[\s]*"
        Dim tnsNamesOraFilePath As String = GetPathToTNSNamesFile()

        If Not tnsNamesOraFilePath.Equals("") Then
            ' Verify file exists
            Dim tnsNamesOraFile As New FileInfo(tnsNamesOraFilePath)
            If tnsNamesOraFile.Exists Then
                If tnsNamesOraFile.Length > 0 Then
                    'read tnsnames.ora file                        
                    Dim tnsNamesContents As String = File.ReadAllText(tnsNamesOraFile.FullName)
                    Dim numMatches As Integer = Regex.Matches(tnsNamesContents, regPattern).Count
                    Dim col As MatchCollection = Regex.Matches(tnsNamesContents, regPattern)
                    For Each match As Match In col
                        Dim m As String = match.ToString()
                        m = m.Trim()
                        DBNamesCollection.Add(m.ToUpper())
                    Next
                End If
            End If
        End If
        Return DBNamesCollection
    End Function

   //Function for Get path of TNS File

    Private Shared Function GetPathToTNSNamesFile() As String
        Dim systemPath As String = Environment.GetEnvironmentVariable("Path")
        Dim reg As New Regex("[a-zA-Z]:\\[a-zA-Z0-9\\]*(oracle|app)[a-zA-Z0-9_.\\]*(?=bin)")
        Dim col As MatchCollection = reg.Matches(systemPath)

        Dim subpath As String = "network\ADMIN\tnsnames.ora"
        For Each match As Match In col
            Dim path As String = match.ToString() & subpath
            If File.Exists(path) Then
                Return path
            End If
        Next
        Return String.Empty
    End Function
End Class

Convert.toString vs .toString ()

2013-01-04T10:19:00.001+05:30

The basic difference between them is “Convert” function handles NULLS.
while “i.ToString()” does not it will throw a NULL reference exception error.

Difference between beginexecutereader and executereader (beginexecutereader Vs executereader)

2012-12-24T11:55:00.001+05:30

The BeginExecuteReader(...) and EndExecuteReader...() are for performing the
ExecuteReader(...) method asynchronously. If you use ExecuteReader(...)
your thread is blocked while that method executes.

Using BeginExecuteReader(...) (and the corresponding EndExecuteReader(...))
ExecuteReader(...) will be executed in a seperate thread, allowing for
yours to continue processing. The BeginExecuteReader(...) method will
require a callback method, and in that callback method, you will make a
call to EndExecuteReader(...) to end the asynchronous operation, and
retreive the return value.

Difference between Correlated subquery and Nested subquery

2012-12-05T15:36:00.003+05:30

Correlated subquery

Correlated subquery runs once for each row selected by the outer query. It contains a reference to a value
from the row selected by the outer query.

Correlated subquery follows down to top approach i.e., main query is executed first(even though parenthesis
are present) and then child query.

We can also say:In a subquery.

Example:

select e1.empname, e1.basicsal, e1.deptno from emp e1

where e1.basicsal = (select max(basicsal) from emp e2 where e2.deptno = e1.deptno)

Nested subquery

Nested subquery runs only once for the entire nesting (outer) query. It does not contain any reference to the
outer query row.

We can also say: in a Correlated subquery,Inner query condition is used in the outer query.

Nested subquery follows top-down approach i.e., child query is executed first and then parent .

Outer query condition is used in the the inner query.

Example:

select empname, basicsal, deptno from emp

where (deptno, basicsal) in (select deptno, max(basicsal) from emp group by deptno)

Difference between thread and process

2012-12-05T15:34:00.003+05:30

Thread

Threads share the address space of the process that created it.
Threads have direct access to the data segment of its process.
Threads can directly communicate with other threads of its process.
Threads have almost no overhead.
New threads are easily created.
Threads can exercise considerable control over threads of the same process
Changes to the main thread (cancellation, priority change, etc.) may affect the behavior of the other threads of the process.

Process

Processes have their own address.
Processes have their own copy of the data segment of the parent process.
Processes must use inter-process communication to communicate with sibling processes.
Processes have considerable overhead.
New processes require duplication of the parent process.
Processes can only exercise control over child processes.
Changes to the parent process does not affect child process.

Difference between trace and debug in .NET

2012-12-05T15:32:00.002+05:30

Trace:

This class works only when your application build defines the symbol TRACE.

For tracing, you have to use Trace.WriteLine statements.

Trace class is generally used to trace the execution during deployment of the application.

Trace class works in both debug mode as well as release mode.

Performance analysis can be done using Trace class.

Trace runs in a thread that is different from the Main Thread.

Trace is used during Testing Phase and Optimization Phase of different releases.

Debug:

This class works only when your application build defines the symbol DEBUG.

For debug, you have to use Debug.WriteLine statements.

You generally use debug classes at the time of development of application.

Debug class works only in debug mode.

Performance analysis cannot be done using Debug class.

Debug runs in the same thread in which your code executes.

Debug is used during Debugging Phase.

Difference between WCF and Web service

2012-10-01T12:42:00.000+05:30

Web service:
The File extension of web service is .asmx.
It can be hosted in IIS.
[WebService] attribute has to be added to the class.
[WebMethod] attribute represents the method exposed to client.
One-way, Request- Response are the different operations supported in web service.
System.Xml.serialization name space is used for serialization.
XML 1.0, MTOM(Message Transmission Optimization Mechanism), DIME, Custom.
Hash Table cannot be serialized.
Only public properties/fields can be serialized.
Unhandled Exceptions returns to the client as SOAP faults.
Slower than WCF.
Uses only SOAP(Simple Object Access Protocol).

WCF:
The file extension of WCF service is .svc.
It can be hosted in IIS, windows activation service, Self-hosting, Windows service.
[ServiceContraact] attribute has to be added to the class.
[OperationContract] attribute represents the method exposed to client.
One-Way, Request-Response, Duplex are different type of operations supported in WCF.
System.Runtime.Serialization namespace is used for serialization.
XML 1.0, MTOM, Binary, Custom.
The DataContractSerializer translate the Hash table into the XML.
Public/Private properties/fields can be serialized.
Better than WebService. The performance measures in terms of xml serialization.
It can send/receive message in any transport protocol message format. By default it uses SOAP for communication.

Difference between Where and Having clauses

2012-10-01T11:55:00.000+05:30

The WHERE clause selects rows before grouping. The HAVING clause selects rows after grouping.
The WHERE clause cannot contain aggregate functions. The HAVING clause can contain aggregate functions.

A HAVING clause is like a WHERE clause, but applies only to groups as a whole, whereas the WHERE clause applies to individual rows. A query can contain both a WHERE clause and a HAVING clause. The WHERE clause is applied first to the individual rows in the tables . Only the rows that meet the conditions in the WHERE clause are grouped. The HAVING clause is then applied to the rows in the result set.

Unable to start debugging. The Silverlight managed debugging package isn’t installed.

2012-09-28T11:07:00.000+05:30

If you ever get the message, well you probably have a configuration problem. So just download and install the Silverlight Developer Run time.

You can get it from here : http://go.microsoft.com/fwlink/?LinkID=188039

It works for me.

Directcast-Vs-Ctype

2012-09-05T05:53:00.000+05:30

By "conversion" mean converting one datatype to another (e.g. string to
integer, decimal to integer, object to string etc).

By "cast" mean changing one type of object into another type that is
related to it by one of the following rules.

ISNULL Vs NULLIF

2012-08-17T17:40:00.002+05:30

ISNULL:
ISNULL ( expression , replacement)
Replaces NULL with the specified replacement value. It returns the value of expression if it is not null.

NULLIF:
NULLIF( expression , expression)
It returns a null value if both the expression is equal. NULLIF returns the first expression if both the expression is not equal.

Virtual Router

2012-07-02T14:31:00.000+05:30

Wifi Hot Spot for Windows 7 / 2008 R2

Virtual Router is a free, open source software based router for PCs running Windows 7 or Windows Server 2008 R2.
Using Virtual Router, users can wirelessly share any internet connection (Wifi, LAN, Cable Modem, Dial-up, Cellular, etc.) with any Wifi device (Laptop, Smart Phone, iPod Touch, iPhone, Android Phone, Zune, Netbook, wireless printer, etc.) These devices connect to Virtual Router just like any other access point, and the connection is completely secured using WPA2 (the most secure wireless encryption.)

Steps for use:

Just Download from link ( http://virtualrouter.codeplex.com/downloads/get/93540 )
Install it.
Restart the system.
Start virtual router.
Connect and use Internet from mobile and Computer through virtual router.

For more refrence please visit:

http://virtualrouter.codeplex.com