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ASP.NET Tutorial - Working with DataSets

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Displaying Cached Data

Considering that there is an Employee’s adress book, that is continuously being used by the employee’s, is not being updated daily with their record. If all the employee want to see the address book page(employee record) the server has to respond to every user. Therefore to save the resources of the webserver for other processing, and to make the program memory resident we the page can be cached in the computer’s cache memory instead of the database.

The following example demonstrates it:

Example 55 CacheAddressbook.aspx

<%@ Import Namespace="System.Data" %>

<%@ Import Namespace="System.Data.SqlClient" %>

<Script Runat="Server">

Sub Page_Load

If Not IsPostBack Then

' Bind to datagrid

dgrdEmployees.DataSource = GetEmployees()

dgrdEmployees.DataBind()

End If

End Sub

Function GetEmployees() As DataView

Dim dstEmployees As DataSet

Dim conNorthwind As SqlConnection

Dim dadEmployees As SqlDataAdapter

Dim dvwEmployees As DataView

dvwEmployees = Cache( "Employees" )

If dvwEmployees Is Nothing Then

dstEmployees = New DataSet()

conNorthwind=New SqlConnection( "Server=localhost; UID=sa;PWD=secret;Database=Northwind" )

dadEmployees = New SqlDataAdapter( "Select * from Employees", conNorthwind )

dadEmployees.Fill( dstEmployees, "Employees" )

dvwEmployees=dstEmployees.Tables("Employees"). DefaultView()

Cache( "Employees" ) = dvwEmployees

End If

Return dvwEmployees

End Function

Sub dgrdEmployees_SortCommand( s As Object, e As DataGridSortCommandEventArgs )

Dim dvwEmployees As DataView

' Sort DataView

dvwEmployees = GetEmployees()

dvwEmployees.Sort = e.SortExpression

' Rebind to DataGrid

dgrdEmployees.DataSource = dvwEmployees

dgrdEmployees.DataBind()

End Sub

</Script>

<html>

<head><title>CacheAddressbook.aspx</title></head>

<body>

<form Runat="Server">

<asp:DataGrid

ID="dgrdEmployees"

AllowSorting="True"

OnSortCommand="dgrdEmployees_SortCommand"

Runat="Server" />

</form>

</body>

</html>

In the above example the DataGrid that displays the list of employee, uses the DataView, returned by the GetEmployees () function as its data source. This function attempts to retrieve a DataView containing the employee’s information from Cache object.

The AllowSorting property of DataGrid is set positive (True) so that the data can be sorted, according to Order by clause of SQL Statements to any column. Moreover even if the database server is stopped then also the page will run, because of its inclusion into the cache memory of the computer. Likewise server resources can be saved for handling other processes.

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