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SqlCacheDependency Class

Establishes a relationship between an item stored in an ASP.NET application's Cache object and either a specific SQL Server database table or the results of a SQL Server 2005 query. This class cannot be inherited.

System.Object
  System.Web.Caching.CacheDependency
    System.Web.Caching.SqlCacheDependency

Namespace:  System.Web.Caching
Assembly:  System.Web (in System.Web.dll)
public sealed class SqlCacheDependency : CacheDependency

The SqlCacheDependency type exposes the following members.

  NameDescription
Public methodSqlCacheDependency(SqlCommand)Initializes a new instance of the SqlCacheDependency class, using the supplied SqlCommand to create a cache-key dependency.
Public methodSqlCacheDependency(String, String)Initializes a new instance of the SqlCacheDependency class, using the supplied parameters to create a cache-key dependency.
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  NameDescription
Public propertyHasChangedGets a value indicating whether the CacheDependency object has changed. (Inherited from CacheDependency.)
Public propertyUtcLastModifiedGets the time when the dependency was last changed. (Inherited from CacheDependency.)
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  NameDescription
Public methodStatic memberCreateOutputCacheDependencyCreates a dependency relationship between an item that is stored in an ASP.NET application's OutputCache object and a SQL Server database table.
Protected methodDependencyDisposeReleases the resources used by the CacheDependency class and any classes that derive from CacheDependency. (Inherited from CacheDependency.)
Public methodDisposeReleases the resources used by the CacheDependency object. (Inherited from CacheDependency.)
Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Protected methodFinishInitCompletes initialization of the CacheDependency object. (Inherited from CacheDependency.)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodGetUniqueIDRetrieves a unique identifier for a SqlCacheDependency object. (Overrides CacheDependency.GetUniqueID().)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Protected methodNotifyDependencyChangedNotifies the base CacheDependency object that the dependency represented by a derived CacheDependency class has changed. (Inherited from CacheDependency.)
Protected methodSetUtcLastModifiedMarks the time when a dependency last changed. (Inherited from CacheDependency.)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
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On all supported versions of SQL Server (Microsoft SQL Server 7.0, Microsoft SQL Server 2000, and SQL Server 2005) the SqlCacheDependency class monitors a specific SQL Server database table. When the table changes, items associated with the table are removed from the Cache, and a new version of the item is added to the Cache.

The SqlCacheDependency class also supports integration with the System.Data.SqlClient.SqlDependency class when using a SQL Server 2005 database. The query notification mechanism of SQL Server 2005 detects changes to data that invalidate the results of an SQL query and removes any cached items associated with the SQL query from the System.Web.Caching.Cache.

You can use the SqlCacheDependency class to add items to your application's Cache that are dependent on either a SQL Server database table or on an SQL query when using SQL Server 2005. You can also use this class with the @ OutputCache directive to make an output-cached page or a user control dependent on a SQL Server database table. Finally, you can use the SqlCacheDependency class with the @ OutputCache page directive to make an output-cached page dependent on the results of an SQL query when using SQL Server 2005. Query notification using SQL Server 2005 is not supported on the @ OutputCache directive for user controls.

NoteNote

For this class to work correctly when using table-based notifications, the database and any tables that you want to make dependencies on must have notifications enabled. You can enable notifications by calling methods of the SqlCacheDependencyAdmin class or by using the Aspnet_regsql.exe command-line tool. In addition, the proper configuration settings must be included in the application's Web.config file.

Using a SqlCacheDependency object with SQL Server 2005 query notification does not require any explicit configuration. Consult the SQL Server 2005 Books Online for information about restrictions on the types of Transact-SQL queries that are allowed when using query notification.

The following example shows an ASP.NET Web.config file that enables table-based dependencies on a SQL Server database table.

<configuration>
  <connectionStrings>
    <add name="Northwind" connectionString="Data Source=(local); Initial Catalog=northwind; Integrated Security=true"; providerName="System.Data.SqlClient" />
  </connectionStrings>
  <system.web>
    <caching>
      <sqlCacheDependency enabled = "true" pollTime = "60000" >
        <databases>
          <add name="northwind" 
            connectionStringName="Northwind"
            pollTime="9000000"
            />
        </databases>
      </sqlCacheDependency>
    </caching>
  </system.web>
</configuration>
TopicLocation
Walkthrough: Using ASP.NET Output Caching with SQL ServerBuilding ASP .NET Web Applications in Visual Studio

The following code example uses the SqlDataSource and GridView controls to display a database table. When the page is loaded, the page attempts to create a SqlCacheDependency object. After the SqlCacheDependency object is created, the page adds an item to the Cache with a dependency on the SqlCacheDependency object. You should use exception handling similar to that shown here.


<%@ Page Language="C#" Debug="true" %>
<%@ import Namespace="System.Data.SqlClient" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<script runat="server">
    public void Page_Load(object Src, EventArgs E) 
    { 
        // Declare the SqlCacheDependency instance, SqlDep. 
        SqlCacheDependency SqlDep = null; 

        // Check the Cache for the SqlSource key. 
        // If it isn't there, create it with a dependency 
        // on a SQL Server table using the SqlCacheDependency class. 
        if (Cache["SqlSource"] == null) { 

            // Because of possible exceptions thrown when this 
            // code runs, use Try...Catch...Finally syntax. 
            try { 
                // Instantiate SqlDep using the SqlCacheDependency constructor. 
                SqlDep = new SqlCacheDependency("Northwind", "Categories"); 
            } 

            // Handle the DatabaseNotEnabledForNotificationException with 
            // a call to the SqlCacheDependencyAdmin.EnableNotifications method. 
            catch (DatabaseNotEnabledForNotificationException exDBDis) { 
                try { 
                    SqlCacheDependencyAdmin.EnableNotifications("Northwind"); 
                } 

                // If the database does not have permissions set for creating tables, 
                // the UnauthorizedAccessException is thrown. Handle it by redirecting 
                // to an error page. 
                catch (UnauthorizedAccessException exPerm) { 
                    Response.Redirect(".\\ErrorPage.htm"); 
                } 
            } 

            // Handle the TableNotEnabledForNotificationException with 
            // a call to the SqlCacheDependencyAdmin.EnableTableForNotifications method. 
            catch (TableNotEnabledForNotificationException exTabDis) { 
                try { 
                    SqlCacheDependencyAdmin.EnableTableForNotifications("Northwind", "Categories"); 
                } 

                // If a SqlException is thrown, redirect to an error page. 
                catch (SqlException exc) { 
                    Response.Redirect(".\\ErrorPage.htm"); 
                } 
            } 

            // If all the other code is successful, add MySource to the Cache 
            // with a dependency on SqlDep. If the Categories table changes, 
            // MySource will be removed from the Cache. Then generate a message 
            // that the data is newly created and added to the cache. 
            finally { 
                Cache.Insert("SqlSource", Source1, SqlDep); 
                CacheMsg.Text = "The data object was created explicitly."; 

            } 
        } 

        else { 
            CacheMsg.Text = "The data was retrieved from the Cache."; 
        } 
    } 
</script>

<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title>ASP.NET Example</title>
</head>
<body>
    <form id="form1" runat="server">
        <p>
        </p>
        <p>
            <asp:SqlDataSource id="Source1" runat="server" SelectCommand="SELECT * FROM [Categories]" UpdateCommand="UPDATE [Categories] SET [CategoryName]=@CategoryName,[Description]=@Description,[Picture]=@Picture WHERE [CategoryID]=@CategoryID" ConnectionString="<%$ ConnectionStrings:Northwind %>"></asp:SqlDataSource>
            <asp:GridView id="GridView1" runat="server" DataKeyNames="CategoryID" AllowSorting="True" AllowPaging="True" DataSourceID="Source1"></asp:GridView>
        </p>
        <p>
        </p>
        <p>
            <asp:Label id="CacheMsg" runat="server" AssociatedControlID="GridView1"></asp:Label>
        </p>
   </form>
</body>
</html>


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
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