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ObjectDataSource.SqlCacheDependency Property

Gets or sets a semicolon-delimited string that indicates which databases and tables to use for the Microsoft SQL Server cache dependency.

Namespace:  System.Web.UI.WebControls
Assembly:  System.Web (in System.Web.dll)

'Declaration
Public Overridable Property SqlCacheDependency As String

Property Value

Type: System.String
A string that indicates which databases and tables to use for the SQL Server cache dependency.

The ObjectDataSource control supports an optional expiration policy that is based on the SqlCacheDependency object for the data cache (the service must be configured for the database server).

SQL Server supports two mechanisms for cache invalidation: polling and notification. Each mechanism has a different syntax for the SqlCacheDependency object.

The ObjectDataSource supports only polling. The SqlCacheDependency string is used to create a SqlDependency object that is passed to the DbCommand constructor before the Select method is executed. The SqlCacheDependency string identifies databases and tables according to the same format that is used by the @ Page directive, where the first part of the string is a connection string to a SQL Server database, followed by a colon delimiter, and finally the name of the database table (for example, "connectionstring1:table1"). If the SqlCacheDependency property depends on more than one table, the connection string and table name pairs are separated by semicolons (for example, "connectionstring1:table1";connectionstring2:table2").

To support notification, you must write the cache logic in the implementation of your SelectMethod property and handle the construction of the SqlCacheDependency object in your code.

This section contains two code examples. The first code example demonstrates how to create a SQL Server cache dependency and set the SqlCacheDependency property of a ObjectDataSource object. The second code example demonstrates how to implement a wrapper method that returns a DataSet object to enable caching and filtering with an ObjectDataSource object.

The following code example demonstrates how to create a SQL Server cache dependency and set the SqlCacheDependency property of a ObjectDataSource control. In this example, the database is polled every 120 seconds. If the data in the Northwind Traders Employees table changes during that time, any data that is cached by the ObjectDataSource control and displayed by the GridView control is expired and a new set of data is retrieved on the next request for the page.

<%@ Register TagPrefix="aspSample" Namespace="Samples.AspNet.VB" Assembly="Samples.AspNet.VB" %>
<%@ Page language="vb" %>

<!--

The page uses an example configuration that includes
connection strings and a defined SqlCacheDependecy.

<?xml version="1.0"?>
<configuration>

  <connectionStrings>
    <add name="MyNorthwind"
         connectionString="Data Source="localhost";Integrated Security="SSPI";Initial Catalog="Northwind""
         providerName="System.Data.SqlClient" />
  </connectionStrings>

  <system.web>
    <cache>
      <sqlCacheDependency enabled="true">
        <databases>
          <add
            name="Northwind"
            connectionStringName="MyNorthwind"
            pollTime="120000" />
        </databases>
      </sqlCacheDependency>
    </cache>

  </system.web>
</configuration>
-->



<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
  <head>
    <title>ObjectDataSource - VB Example</title>
  </head>
  <body>
    <form id="Form1" method="post" runat="server">

        <asp:gridview
          id="GridView1"
          runat="server"
          datasourceid="ObjectDataSource1" />

        <asp:objectdatasource
          id="ObjectDataSource1"
          runat="server"
          typename="Samples.AspNet.VB.EmployeeLogic"
          selectmethod="GetAllEmployeesAsDataSet"
          enablecaching="True"
          cacheduration="300"
          cacheexpirationpolicy="Absolute"
          sqlcachedependency="Northwind:Employees" />

    </form>
  </body>
</html>

The following code example demonstrates how to implement a wrapper method that returns a DataSet object to enable caching and filtering with an ObjectDataSource control. In the base implementation of the EmployeeLogic class, the GetAllEmployees method returns an ArrayList object. Instead of refactoring the object completely to work with the ObjectDataSource on a Web Forms page, a wrapper method named GetAllEmployeesAsDataSet is added that returns a set of NorthwindEmployee data as a DataSet.

Imports System
Imports System.Collections
Imports System.Configuration
Imports System.Data
Imports System.Data.SqlClient
Imports System.Web.UI
Imports System.Web.UI.WebControls

Namespace Samples.AspNet.VB

' EmployeeLogic is a stateless business object that encapsulates 
' the operations one can perform on a NorthwindEmployee object. 

Public Class EmployeeLogic

   ' Returns a collection of NorthwindEmployee objects. 
   Public Shared Function GetAllEmployees() As ICollection
      Dim al As New ArrayList()

      Dim cts As ConnectionStringSettings = ConfigurationManager.ConnectionStrings("NorthwindConnection")

      Dim sds As New SqlDataSource(cts.ConnectionString, "SELECT EmployeeID FROM Employees")

      Try 
         Dim IDs As IEnumerable = sds.Select(DataSourceSelectArguments.Empty)

         ' Iterate through the Enumeration and create a 
         ' NorthwindEmployee object for each ID. 
         Dim enumerator As IEnumerator = IDs.GetEnumerator()
         While enumerator.MoveNext()
            ' The IEnumerable contains DataRowView objects. 
            Dim row As DataRowView = CType(enumerator.Current,DataRowView)
            Dim id As String = row("EmployeeID").ToString()
            Dim nwe As New NorthwindEmployee(id)
            ' Add the NorthwindEmployee object to the collection.
            al.Add(nwe)
         End While 
      Finally 
         ' If anything strange happens, clean up.
         sds.Dispose()
      End Try 

      Return al
   End Function 'GetAllEmployees

   ' To support basic filtering, the employees cannot 
   ' be returned as an array of objects, rather as a 
   ' DataSet of the raw data values. 
   Public Shared Function GetAllEmployeesAsDataSet() As DataSet
      Dim employees As ICollection = GetAllEmployees()

      Dim ds As New DataSet("Table")

      ' Create the schema of the DataTable. 
      Dim dt As New DataTable()
      Dim dc As DataColumn
      dc = New DataColumn("FirstName", GetType(String))
      dt.Columns.Add(dc)
      dc = New DataColumn("LastName", GetType(String))
      dt.Columns.Add(dc)
      dc = New DataColumn("Title", GetType(String))
      dt.Columns.Add(dc)
      dc = New DataColumn("Courtesy", GetType(String))
      dt.Columns.Add(dc)
      dc = New DataColumn("Supervisor", GetType(Int32))
      dt.Columns.Add(dc)

      ' Add rows to the DataTable. 
      Dim emplEnum As IEnumerator = employees.GetEnumerator()
      Dim row As DataRow
      Dim ne As NorthwindEmployee
      While emplEnum.MoveNext()
         ne = CType(emplEnum.Current, NorthwindEmployee)
         row = dt.NewRow()
         row("FirstName") = ne.FirstName
         row("LastName") = ne.LastName
         row("Title") = ne.Title
         row("Courtesy") = ne.Courtesy
         row("Supervisor") = ne.Supervisor
         dt.Rows.Add(row)
      End While 
      ' Add the complete DataTable to the DataSet.
      ds.Tables.Add(dt)

      Return ds
   End Function 'GetAllEmployeesAsDataSet

   Public Shared Function GetEmployee(anID As Object) As NorthwindEmployee
      If anID.Equals("-1") OrElse anID.Equals(DBNull.Value) Then 
         Return New NorthwindEmployee()
      Else 
         Return New NorthwindEmployee(anID)
      End If 
   End Function 'GetEmployee


   Public Shared Sub UpdateEmployeeInfo(ne As NorthwindEmployee)
      Dim retval As Boolean = ne.Save()
      If Not retval Then 
         Throw New NorthwindDataException("UpdateEmployee failed.")
      End If 
   End Sub 'UpdateEmployeeInfo

   Public Shared Sub DeleteEmployee(ne As NorthwindEmployee)
      Dim retval As Boolean = ne.Delete()
      If Not retval Then 
         Throw New NorthwindDataException("DeleteEmployee failed.")
      End If 
   End Sub 'DeleteEmployee
End Class 'EmployeeLogic


Public Class NorthwindEmployee


   Public Sub New()
      ID = DBNull.Value
      aLastName = ""
      aFirstName = ""
      aTitle = ""
      titleOfCourtesy = ""
      reportsTo = - 1
   End Sub 'New 


   Public Sub New(anID As Object)
      Me.ID = anID

      Dim cts As ConnectionStringSettings = ConfigurationManager.ConnectionStrings("NorthwindConnection")

      Dim conn As New SqlConnection(cts.ConnectionString)

      Dim sc As New SqlCommand(" SELECT FirstName,LastName,Title,TitleOfCourtesy,ReportsTo " & _
                               " FROM Employees " & _
                               " WHERE EmployeeID = @empId", conn)
      ' Add the employee ID parameter and set its value.
      sc.Parameters.Add(New SqlParameter("@empId", SqlDbType.Int)).Value = Int32.Parse(anID.ToString())
      Dim sdr As SqlDataReader = Nothing 

      Try
         conn.Open()
         sdr = sc.ExecuteReader()

         ' Only loop once. 
         If Not (sdr Is Nothing) AndAlso sdr.Read() Then 
            ' The IEnumerable contains DataRowView objects. 
            Me.aFirstName = sdr("FirstName").ToString()
            Me.aLastName = sdr("LastName").ToString()
            Me.aTitle = sdr("Title").ToString()
            Me.titleOfCourtesy = sdr("TitleOfCourtesy").ToString()
            If Not sdr.IsDBNull(4) Then 
               Me.reportsTo = sdr.GetInt32(4)
            End If 
         Else 
            Throw New NorthwindDataException("Data not loaded for employee id.")
         End If 
      Finally 
         Try 
            If Not (sdr Is Nothing) Then
               sdr.Close()
            End If
            conn.Close()
         Catch se As SqlException
            ' Log an event in the Application Event Log. 
            Throw 
         End Try 
      End Try 
   End Sub 'New 

   Private ID As Object 
   Public ReadOnly Property EmpID() As String 
      Get 
         Return ID.ToString()
      End Get 
   End Property 

   Private aLastName As String 
   Public Property LastName() As String 
      Get 
         Return aLastName
      End Get 
      Set
         aLastName = value
      End Set 
   End Property 

   Private aFirstName As String 
   Public Property FirstName() As String 
      Get 
         Return aFirstName
      End Get 
      Set
         aFirstName = value
      End Set 
   End Property 

   Public ReadOnly Property FullName() As String 
      Get 
         Return FirstName & " " & LastName
      End Get 
   End Property 

   Private aTitle As String 
   Public Property Title() As String 
      Get 
         Return aTitle
      End Get 
      Set
         aTitle = value
      End Set 
   End Property 

   Private titleOfCourtesy As String 
   Public Property Courtesy() As String 
      Get 
         Return titleOfCourtesy
      End Get 
      Set
         titleOfCourtesy = value
      End Set 
   End Property 

   Private reportsTo As Integer 
   Public Property Supervisor() As Integer 
      Get 
         Return reportsTo
      End Get 
      Set
         reportsTo = value
      End Set 
   End Property 

   Public Function Save() As Boolean 

      ' Implement persistence logic. 
      Return True 

   End Function 'Save


   Public Function Delete() As Boolean 

      ' Implement delete logic. 
      Return True 

   End Function 'Delete
End Class 'NorthwindEmployee


Friend Class NorthwindDataException
   Inherits Exception

   Public Sub New(msg As String)
      MyBase.New(msg)
   End Sub 'New 
End Class 'NorthwindDataException
End Namespace

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0
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