Dotnet Source Code

What is a Typed Dataset in ADO.NET? Why do we use a Typed DataSet? What is the difference between a Typed and an UnTyped DataSet?

2009-11-21T03:53:00.001-08:00

Typed DataSet - When a created DataSet derives from the DataSet class, that applies the information contained in the XSD to create a Typed class, this DataSet is said to be a Typed Dataset. Information from the schema whic comprises the tables, columns, and rows is created and compiled to a new DataSet derived from the XSD. The Typed DataSet class features all functionality of the DataSet class. This may be used with methods that take an instance of the DataSet class as a parameter.

Note that an UnTyped DataSet does not have any schema. It is exposed simply as a mere collection.

How to create a Typed DataSet? -
Write click your project in the Solution Explorer.
Click Add New Item.
Select DataSet.

This adds a new XSD to the project. The schema created may be viewed as an XML. When this xsd file is compiled, two files are created by Visual Studio. The first file that contains the .vb or .cs extension contains the information about the proxy class. This class contains methods & properties that are required to access the database
data. The second file has an extension xsx and this contains information about the layout of the XSD.

What is Diffgram in ADO.NET? When do we use Diffgram?

2009-11-21T03:52:00.003-08:00

A DiffGram is an XML format. It is used to identify current and original versions of data elements. A DataSet may use a DiffGram format to load and persist the contents, and further to serialize its contents for porting across a network connection. Whenever a DataSet is written as a DiffGram, the DataSet populates the DiffGram with all the important information to accurately recreate the contents. Note that schema of the DataSet is not recreated. This includes column values from both the Current and the Original row versions, row error information, and row order.

What is DataRelation object in ADO.NET? How to use a DataRelation between two columns in ADO.NET?

2009-11-21T03:52:00.001-08:00

In order to set the relationship between two or more than two columns, ADO.NET provides the DataRelation class. When a DataRelation object is created, it assists to enforce some constraints on the relationships between columns. The constraint may be like a Unique constraint that ensures that a column will have no duplicate value in the table. A Foreign Key constraint may be used to enforce Referential Integrity. The Unique property may be set by setting the Unique property of a DataColumn to True. This may also be done by adding an instance of the UniqueConstraint class to the DataRelation object. As a part of the foreign key constraint, we may specify referential integrity rules that are applied at 3 places

1) When a parent record is updated
2) When a parent record is deleted
3) When a change is rejected or accepted.

A DataRelation object permits to establish a parent-child relationship between two or more tables inside a DataSet object. The easiest way to create a DataRelation between two tables in a DataSet is to setup a primary key - foreign key relationship between the columns of a table.

See code example below, where a DataRelation has been setup between the Employee table and the Salary table...

'Code Below in VB.NET
Dim Conn As SqlConnection
Dim da As SqlDataAdapter
Dim ds As DataSet
Dim RowParent As DataRow
Dim RowChild As DataRow

Conn = New _
SqlConnection(ConfigurationSettings.Appsettings("SomeConnectionStringWrittenInWeb.Config"))
da = New SqlDataAdapter("SELECT * FROM Employees", Conn)
ds = New DataSet()

Try
Conn.Open()
da.Fill( ds,"Employees")
da.SelectCommand = New SqlCommand("SELECT * FROM Salary", Conn)
da.Fill(ds, "Salary")
Catch ex As SqlException
Response.Write(ex.ToString())
Finally
Conn.Dispose()
End Try

'Next, Let us create a Data Relationship
ds.Relations.Add("Employee_Salary", ds.Tables("Employees").Columns("EmployeeID"), _
ds.Tables("Salary").Columns("EmployeeID"))
'Display the Employee and Child Salary in the Form
'Say we have a Label in the form
For each RowParent in ds.Tables("Employees").Rows

lblRelation.Text &= RowParent("Emp_Name")
For each RowChild in RowParent.GetChildRows("Employee_Salary")
lblRelation.Text &= "
" & RowChild("Sal_Amount")
Next
Next

What is a DataView in ADO.NET?

2009-11-21T03:51:00.004-08:00

DataView - Just like we have Views in SQL (in our backend), we have DataView object in ADO.NET. A dataview object represents bindable, customized view of a DataTable object. Operations like Sorting, Filtering, Searching, Editing and Navigation may be performed on a DataView object. In scenarios like retrieval of a subset of data from a Datatable, we may make use of DataViews to get this data. Note that the DefaultView property of a DataTable returns the Default data view for the DataTable. In case a custom view of a DataTable has to be created on a DataView, then the RowFilter property of the DataView is set to the DefaultView.

A dataview may also be used to sort data that resides in it in ascending or descending order. Below is code on how to sort data in a dataview in ascending or descending order...

DataView objdv = new DataView();
objdv.Sort("ColumnName Asc|Desc");

What is a SqlCommandBuilder in ADO.NET

2009-11-21T03:51:00.002-08:00

SqlCommandBuilder class in ADO.NET provides the feature of reflecting the changes made to a DataSet or an instance of the SQL server data. When an instance of the SqlCommandBuilder class is created, it automatically generates Transact-SQL statements for the single table updates that occur. The object of the SqlCommandBuilder acts as a listener for RowUpdating events, whenever the DataAdapter property is set.

The SqlCommandBuilder object automatically generates the values contained within the SqlDataAdapter's InsertCommand, UpdateCommand and DeleteCommand properties based on the initial SelectCommand. The advantage here is that you will not need to write SqlCommand & SqlParameter Types explicitly.

Basically the command builder object builds these objects on the fly. The command builder object actually reads the metadata of the method called. After the builder object reads the underlying schema of the adapter's method, it autogenerates an underlying insert, update & delete command object. See code example below...

//Code below in C#...
DataSet ds = new DataSet();
SqlConnection cn = new SqlConnection("strSomeConnectionString");
//Autogenerate Insert, Update & Delete commands
SqlDataAdapter da = new SqlDataAdapter("Select from t_Something", cn);
SqlCommandBuilder scb = new SqlCommand(da);

//Fill the dataset
da.Fill(ds,"t_Something");

What is SelectCommand in ADO.NET?

2009-11-21T03:51:00.000-08:00

Select Command Property - This property is used to hold the SQL command that is used to retrieve data from the data source. The CommandText and Connection are properties of the Select Command propety. CommandType is also a property of Select Command. See example below...

Dim da as new SqlDataAdapter
da.SelectCommand = New SqlCommand( )
With da.SelectCommand
.Connection = objConnection
.CommandText = "select * from employees"
End With

What is a command object in ADO.NET. How to use a command object in .NET?

2009-11-21T03:50:00.002-08:00

ADO.NET Command Object - The Command object is similar to the old ADO command object. It is used to store SQL statements that need to be executed against a data source. The Command object can execute SELECT statements, INSERT, UPDATE, or DELETE statements, stored procedures, or any other statement understood by the database. See sample code...

'Code below in VB.NET
...
Dim ObjCom as SqlClient.SqlCommand
ObjCom.SqlConnection(strCon)
ObjCom.Connection.Open()
ObjCom.CommandText = "Select * from tblSample"
ObjCom.ExecuteNonQuery()

SqlCommand objects are not used much when we use datasets and data adapters. Following are some properties of the SqlCommand class...

Connection Property - This property contains data about the connection string. It must be set on the SqlCommand object before it is executed. For the command to execute properly, the connection must be open at the time of execution.

CommandText Property - This property specifies the SQL string or the Stored Procedure.

objCom.CommandText = "Insert into Employees (empid, empname) values ('EMI0334','Mandy')"

Paramaters Collection - If we want to update values in the Employees table above, but we do not know the values at design time, we make use of placeholders. These are variables prefixed with "@" symbol. Our code will look like this...

objCom.CommandText = "Insert into Employees (empid, empname) values (@empid, @empname)

Next, we have to create parameters that will be used to insert values into the placeholders. For this, we need to add parameters to the parameters collection of the SqlCommand object. This is done so that the values added through the parameters collection & placeholders get i ncluded in the SQL statement. Here, parameters mean the parameters to be passed to the SQL statement/Stored Procedures, not the method's parameters.

In order to add parameters to the SqlCommand object, we write the following code...

objCom.CommandText = "Insert into Employees (empid, empname) values (@empid, @empname)"

objCom.Parameters.Add("@empID", txtempid.text)

objCom.Parameters.Add("@empname", txtempname.text)

ExecuteNonQuery Method - Once the connection is open, we run the query in the SqlCommand object using the ExecuteNonQuery method. This is very simple as shown below...

objConnection.Open()
objCom.ExecuteNonQuery()
objConnection.Close()

What is a connection object in ADO.NET? How to connect to a database in .Net?

2009-11-21T03:50:00.000-08:00

A Connection object in ADO.NET is used to establish a connection between a program (the program may be a windows page, a web page, a windows service, a web service etc.) and the database. The connection is open just long enough to get or update data. By quickly opening, then closing a connection, the server resources are used as little as possible. See code below on how to open a connection between UI and database...

'Code below in VB.NET ...
Dim objectConn as SqlClient.SqlConnection
Dim strConn as String
Try
'First, create a connection object
objectConn=New SqlClient.SqlConnection()

'Next, build the Connection String
strConn &="Data Source=(local
strConn &="Initial Catalog=DatabaseName;"
strConn &= "User ID=admin;"
strConn &= "Password=;"

'Note here that the connection string may also be passed as a parameter
'to the connection string object during instantiation

objectConn.ConnectionString = strConn
objectConn.Open() 'Open the Connection

'The connection is now open
'Write your vb.net code here for operations on the database
objectConn.Close()

Catch Ex As Exception
MessageBox.Show(Ex.Message)
End Try

CONNECTION STRINGS FOR ACCESS, SQL 2000, SQL 2005, Oracle, MySQL

What are Connection Strings - A connection string has a group of semi-colon-separated attributes. Every .Net Data Provider connection string looks different, depending on the type of .NET Data Provider you need to use and which attributes are set for each different type of database system. An example, the connection string below is an example of what you use to connect to a local SQL Server. See that every parameter is separated by a semicolon.

Data Source=(local);Initial Catalog=Northwind;User ID=sa;Password=;

The connection string shown below is an example of how to connect to a Microsoft Access 2000 database using the OleDbConnection object in System.Data.OleDb.

Provider=Microsoft.Jet.OleDb.4.0;Data Source=C:\Northwind.mdb

Parameters in a Connection String - The parameters depend on the data provider is being used.

Server - The name of the SQL Server to which connection has to be established through ADO.NET. This is the name of the system that is running SQL server. We may use "local" or "localhost" for local computer. In case we are using named instances of SQL server, then the parameter would contain the computer name, followed by a backslash, followed by a named instance of the SQL server.

Database - The name of the database to which connection is to be established.

User ID - A user ID configured in the SQL Server by the SQL Server administrator.

Password - As the attribute name suggests, this is the password associated with the user id.

Note that connection string may also contain the Windows NT account security settings. This is done by passing the paramater "integrated security=true".

What is ADO.NET?

2009-11-21T03:49:00.000-08:00

ADO.NET is a part of the Microsoft .NET Framework. This framework provides the set of classes that deal with data communication between various layers of the software architecture and the database. It provides a continious access to different data source types such as SQL Server versions 7, 2000, 2005. It also provides connectivity options to data sources through OLE DB and XML. Connectivity may be established with other databases like Oracle, MySQL etc. as well.

ADO.NET has the ability to separate data access mechanisms, data manipulation mechanisms and data connectivity mechanisms.

ADO.NET introduces along with it the disconnected architecture. In a disconncted architecture, data may be stored in a DataSet. It contains providers for connecting to databases, commands for execution and retrieval of results.

The classes for ADO.NET are stored in the DLL System.Data.dll.

What is a bubbled event in ASP.NET server side controls

2009-10-13T02:21:00.003-07:00

Bubbling an Event
The ASP.NET page framework provides a technique called event bubbling that allows a child control to propagate events up its containment hierarchy. Event bubbling enables events to be raised from a more convenient location in the controls hierarchy and allows event handlers to be attached to the original control as well as to the control that exposes the bubbled event.

Event bubbling is used by the data-bound controls (Repeater, DataList, and DataGrid) to expose command events raised by child controls (within item templates) as top-level events. While ASP.NET server controls in the .NET Framework use event bubbling for command events (events whose event data class derives from CommandEventArgs), any event defined on a server control can be bubbled.

What is smart navigation in ASP.NET Pages

2009-10-13T02:21:00.001-07:00

When a page is requested by an Internet Explorer 5 browser, or later, smart navigation enhances the user's experience of the page by performing the following:
• Eliminating the flash caused by navigation.
• Persisting the scroll position when moving from page to page.

• Persisting element focus between navigations.
• Retaining only the last page state in the browser's history.
• Smart navigation is best used with ASP.NET pages that require frequent postbacks but with visual content that does not change dramatically on return. Consider this carefully when deciding whether to set this property to true.
Set the SmartNavigation attribute to true in the @ Page directive in the .aspx file. When the page is requested, the dynamically generated class sets this property.

What are main parts of ASP.NET

2009-10-13T02:20:00.003-07:00

• A page and controls framework (Web Forms)
• The ASP.NET compiler
• Security infrastructure
• State-management facilities
• Application configuration

• Health monitoring and performance features
• Debugging support
• An XML Web services framework
• Extensible hosting environment and application life cycle management
• An extensible designer environment

What is the difference between code inline and code behind models in Asp.Net

2009-10-13T02:20:00.001-07:00

Code-Inline model in Asp.Net
In Code-Inline model the code & event handlers for the controls are located in blocks in the same .aspx file that contains the HTML and controls. Code-Inline model is useful when you want to maintain your code and presentation logic in a single file.

Code-behind model in Asp.Net
ASP.NET also supports another way to factor your code and presentation content, called the code-behind model. When using code-behind, the code for handling events is located in a physically separate file from the page that contains server controls and markup. This clear delineation between code and content is useful when you need to maintain these separately, such as when more than one person is involved in creating the application. It is often common in group projects to have designers working on the UI portions of an application while developers work on the behavior or code. The code-behind model is well-suited to that environment.

What are the ways to manage state in Asp.Net application

2009-10-13T02:19:00.005-07:00

Ways to manage state in Asp.Net are:
• Using Session and Application objects to cache information.
• Using Memory and Disk Cookies to preserve information.
• Using hidden input fields or the URL -embedded information to pass information from one page to another.

• Using the ViewState property of the page to set and retrieve information stored in a StateBag object.
• Using SQL Server to store state information.

Explain the limitation & issues with the Cookies

2009-10-13T02:19:00.003-07:00

Limitation & Issues with Cookies
Using cookies gives you excellent state management capabilities, as they are simple to implement, and they help you move resources off the server. Like almost any particular technique, cookies have some limitations.

Some Users Dont Allow Cookies
Some users believe that viruses can be sent in a cookie and will not allow them onto their computers. Although there have never been any documented cases of this happening, and no one could realistically send a virus through a cookie, a lot of users still turn off the ability to accept cookies. When this happens, the user will not be able to use your site if you use cookies for managing state.

Performance Can Deteriorate
Imagine that a user walks through a wizard on your site, as you gather 100 pieces of data from that user over several pages. Each page needs to post gathered data to the server. If you wait until all 100 pieces of data are gathered, you need to store that data somewhere in the meantime. If you keep putting data into a cookie, there is a lot of data being sent back and forth between the browser and the server. This will eat up a lot of bandwidth and could slow your whole site down. Remember, the data has to go both ways for each page the users hit on your site.

Cookies Take Up Memory
Some browsers impose a limit on the size of the cookie data they can accept, or the number of cookies they can accept at one time. In addition, the amount of memory that you may chew up on the users machine may cause their operating system to swap some memory to disk. Under this circumstance, the cookie has slowed down your users machine as well as the server.

Explain the Limitations & Issues with Automatic SQL Server State Management

2009-10-13T02:19:00.001-07:00

• Although using SQL Server to store your session state relieves you of many difficult development issues, youll still need to consider some important limitations:
• Youre limited to SQL Server.
• This technique can only use SQL Server, no other server database. If you do not have a SQL Server installation available, you will be unable to use this solution.

• Performance may suffer.
• Like any of the state management techniques, using SQL Server to manage your applications state can cause your performance degrade a little. Because it takes a little bit of time to make a connection and read and write state information in the database, theres no avoiding a small bit of overhead.

What is the purpose of Server.MapPath method in Asp.Net

2009-10-13T02:18:00.007-07:00

In Asp.Net Server.MapPath method maps the specified relative or virtual path to the corresponding physical path on the server. Server.MapPath takes a path as a parameter and returns the physical location on the hard drive.

Syntax
Suppose your Text files are located at D:\project\MyProject\Files\TextFiles

If the root project directory is MyProject and the aspx file is located at root then to get the same path use code

/* physical path of TextFiles */
string TextFilePath=Server.MapPath("Files/TextFiles");

What is difference between Response.Redirect and Server.Transfer

2009-10-13T02:18:00.003-07:00

Response.Redirect vs Server.Transfer

Server.Transfer or Response.Redirect both are the method of choice for transferring the user from one place in the application to another

Server.Transfer is similar in that it sends the user to another page with a statement such as Server.Transfer("WebForm2.aspx"). However, the statement has a number of distinct advantages and disadvantages.

Firstly, transferring to another page using Server.Transfer conserves server resources. Instead of telling the browser to redirect, it simply changes the "focus" on the Web server and transfers the request. This means you don't get quite as many HTTP requests coming through, which therefore eases the pressure on your Web server and makes your applications run faster.

But watch out: because the "transfer" process can work on only those sites running on the server, you can't use Server.Transfer to send the user to an external site. Only Response.Redirect can do that.

The other side debates that Server.Transfer is not user friendly because the page requested may not be the page that shows in the URL. Response.Redirect is more user-friendly, as the site visitor can bookmark the page that they are redirected to.

Secondly, Server.Transfer maintains the original URL in the browser. This can really help streamline data entry techniques, although it may make for confusion when debugging.

That's not all: The Server.Transfer method also has a second parameter"preserveForm". If you set this to True, using a statement such as Server.Transfer("WebForm2.aspx", True), the existing query string and any form variables will still be available to the page you are transferring to.

For example, if your WebForm1.aspx has a TextBox control called TextBox1 and you transferred to WebForm2.aspx with the preserveForm parameter set to True, you'd be able to retrieve the value of the original page TextBox control by referencing Request.Form("TextBox1").

Explain the concept of Web Application

2009-10-13T02:18:00.001-07:00

An introduction to web applications
A web application consists of a set of web pages that are generated in response to user requests. The Internet has many different types of web applications, such as search engines, online stores, auctions, news sites, discussion groups, games, and so on.
Properties of web applications
• Web applications are a type of client/server application. In that type of application, a user at a client computer accesses an application at a server computer. In a web application, the client and server computers are connected via the Internet or via an intranet (a local area network).
• In a web application, the user works with a web browser at the client computer. The web browser provides the user interface for the application. The most popular web browsers are Microsofts Internet Explorer, .Mozilla Firefox

• The application runs on the server computer under the control of web server software. For ASP.NET web applications, the server must run Microsofts web server, called Internet Information Services, or IIS.
• For most web applications, the server computer also runs a database management system, or DBMS, such as Microsofts SQL Server. The DBMS provides access to information stored in a database. To improve performance on larger applications, the DBMS can be run on a separate server computer.
• The user interface for a web application is implemented as a series of web pages that are displayed in the web browser. Each web page is defined by a web form using HTML, or Hypertext Markup Language, which is a standardized set of markup tags.
• The web browser and web server exchange information using HTTP (Hypertext Transfer Protocol).

What is LoginView control in ASP.NET

2009-10-13T02:17:00.005-07:00

LoginView Control: This control provides templates in which you can create different content for anonymous and authenticated users. The LoginView control is also role-aware, so you can actually create different templates for authenticated users in different roles.

The control displays one of two templates: the AnonymousTemplate or the LoggedInTemplate. In the templates, you can add markup and controls that display information appropriate for anonymous users and authenticated users, respectively.

The LoginView control also includes events for ViewChanging and ViewChanged, which allow you to write handlers for when the user logs in and changes status.

What is the use of PasswordRecovery control in ASP.NET

2009-10-13T02:17:00.003-07:00

PasswordRecovery Control: This control provides the user interface and corresponding functionality to help users retrieve or reset their passwords. The control has three views: User- name, Question, and Success. The Username view allows the user to enter the username for which a password has to be retrieved or reset. The Question view prompts the user for the answer to a question that was entered during registration. The Success view displays a success message after the password has been delivered via e-mail.

The options available for password retrieval are determined in part by the Membership provider used to provide membership services. ASP.NET 2.0 includes a provider for Microsoft SQL Server. This support password retrieval and security questions. Other providers, such as a third-party offerings or one you create yourself, might not support all those features. Also, the default the built-in providers to stores password hashes. (Clear text and encrypted text are the other options.) Password hashes cannot be used to determine the original password, so by default the only recovery scheme available is to reset the password and e-mail the new password to the user.

What is LoginStatus control in ASP.NET

2009-10-13T02:17:00.001-07:00

LoginStatus Control: This control produces a Login or Logout hyperlink based on the login status of the current user: an anonymous user sees a Login link, and an authenticated user sees a Logout link. The actual text for the hyperlink as well as the target of the link is, of course, customizable.

The Logout link can be configured to do one of three things after the user has logged out: refresh the current page, redirect the user to the login page, or redirect the user to some other page.

What is ChangePassword control in ASP.NET

2009-10-13T02:16:00.007-07:00

The ChangePassword control allows users to change their password. The user must first supply the original password and then create and confirm the new password. If the original password is correct, the user password is changed to the new password. The control also includes support for sending an e-mail message about the new password.

The ChangePassword control includes two templated views that are displayed to the user. The first is the ChangePasswordTemplate, which displays the user interface used to gather the data required to change the user password. The second template is the SuccessTemplate, which defines the user interface that is displayed after a user password has been successfully changed.

The ChangePassword control works with authenticated and non-authenticated users. If a user has not been authenticated, the control prompts the user for a login name. If the user is authenticated, the control populates the text box with the user's login name.

What is LoginName control in ASP.NET

2009-10-13T02:16:00.005-07:00

LoginName control: This control is a placeholder that displays the username of the user. If the current user is anonymous (that is, not authenticated), this control does not render any output.

The LoginName exposes a FormatString property that you can use to display more than just the username. For example, the FormatString could be set to "Welcome, {0}", which would produce the output "Welcome, John" when John is logged in.

What is the use of CreateUserWizard control in ASP.NET

2009-10-13T02:16:00.003-07:00

CreateUserWizard Control: This control provides a wizard-style interface for creating a new user in the membership system. The CreateUserWizard is a lot more than a simple form for entering a username and password. It includes field validation for all of its fields, including optional regular expression validation for e-mail addresses. It prompts the user to enter a proposed password twice and confirms that the passwords match.

The CreateUserWizard control can also gather a security question and answer from the user if the underlying membership provider supports security questions. The "Walkthrough" section for this application also shows how you can add custom steps to the wizard to collect additional information from the user during registration.