Provides a way to specify a custom LINQ query that is called in response to an event.
System.Web.UI.WebControls.Expressions.DataSourceExpression
System.Web.UI.WebControls.Expressions.ParameterDataSourceExpression
System.Web.UI.WebControls.Expressions.CustomExpression
Namespace: System.Web.UI.WebControls.Expressions
Assembly: System.Web.Extensions (in System.Web.Extensions.dll)
Public Class CustomExpression _ Inherits ParameterDataSourceExpression
public class CustomExpression : ParameterDataSourceExpression
public ref class CustomExpression : public ParameterDataSourceExpression
type CustomExpression = class inherit ParameterDataSourceExpression end
The CustomExpression type exposes the following members.
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CustomExpression | Initializes a new instance of the CustomExpression class. |
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Context | Gets the HttpContext instance of the owner control. (Inherited from DataSourceExpression.) |
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DataSource | Gets the data source object that is associated with the owner control. (Inherited from DataSourceExpression.) |
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IsTrackingViewState | Gets a value that indicates whether a data source expression object is tracking its view state changes. (Inherited from DataSourceExpression.) |
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Owner | Gets the owner control. (Inherited from DataSourceExpression.) |
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Parameters | Gets the parameters that are associated with this DataSourceExpression object. (Inherited from ParameterDataSourceExpression.) |
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ViewState | Gets an instance of the StateBag class that contains the current view state information. (Inherited from DataSourceExpression.) |
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Equals(Object) | Determines whether the specified Object is equal to the current Object. (Inherited from Object.) |
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Finalize | Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.) |
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GetHashCode | Serves as a hash function for a particular type. (Inherited from Object.) |
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GetQueryable | Provides access to the modified IQueryable object that the data source uses. (Overrides DataSourceExpression.GetQueryable(IQueryable).) |
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GetType | Gets the Type of the current instance. (Inherited from Object.) |
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LoadViewState | Loads the state of the values in the ParameterDataSourceExpression object that must be persisted. (Inherited from ParameterDataSourceExpression.) |
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MemberwiseClone | Creates a shallow copy of the current Object. (Inherited from Object.) |
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SaveViewState | Saves the current view state of the ParameterDataSourceExpression object. (Inherited from ParameterDataSourceExpression.) |
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SetContext | Executes the expression by using the specified owner control, context, and data source. (Inherited from ParameterDataSourceExpression.) |
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SetDirty | Marks the DataSourceExpression object so that its state will be saved in view state. (Inherited from DataSourceExpression.) |
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ToString | Returns a string that represents the current object. (Inherited from Object.) |
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TrackViewState | Tracks view-state changes of the ParameterDataSourceExpression object so that the changes can be stored in the StateBag object for the object. (Inherited from ParameterDataSourceExpression.) |
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Querying | Occurs when the IQueryable data source value is set. |
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IStateManager.IsTrackingViewState | When implemented by a class, gets a value that indicates whether a data source expression object is tracking its view state changes. (Inherited from DataSourceExpression.) |
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IStateManager.LoadViewState | When implemented by a class, loads the previously saved view state of the data source expression object. (Inherited from DataSourceExpression.) |
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IStateManager.SaveViewState | When implemented by a class, saves the current view state of the DataSourceExpression object. (Inherited from DataSourceExpression.) |
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IStateManager.TrackViewState | When implemented by a class, tracks view state changes of the DataSourceExpression object so that the changes can be stored in the StateBag object for the data source expression object. (Inherited from DataSourceExpression.) |
The CustomExpression class is used with the QueryExtender control. The QueryExtender control supports a variety of options that you can use to filter data. The QueryExtender control supports filters that let you search strings, search values between a specified range, compare a property value in a table to a specified value, and sort data. These options are provided as LINQ expressions in the QueryExtender control. You can use these filter expressions or you can provide a custom expression that you can use in the QueryExtender control. The CustomExpression class enables you to specify a custom expression in your application and call it in an event handler.
Note
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You can provide a custom query that is called by a method instead of an event handler by using the MethodExpression class. |
The following example shows how to create a CustomExpression object that is used by the QueryExtender control. The custom expression calls the FilterProducts method, which contains a custom LINQ expression. The result of the filtering operation is displayed in a GridView control.
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Custom Filter</title>
</head>
<body>
<form id="form1" runat="server">
<div>
</div>
<asp:LinqDataSource ID="LinqDataSource1" runat="server"
ContextTypeName="AdventureWorksDataContext" EntityTypeName=""
TableName="Products">
</asp:LinqDataSource>
<asp:QueryExtender ID="QueryExtender1" runat="server" TargetControlID="LinqDataSource1">
<asp:CustomExpression OnQuerying="FilterProducts"></asp:CustomExpression>
</asp:QueryExtender>
<asp:GridView ID="GridView1" runat="server"
DataSourceID="LinqDataSource1"
DataKeyNames="ProductID" AllowPaging="True">
</asp:GridView>
</form>
</body>
</html>
The following example shows an event handler that contains a custom LINQ query. The expression filters the Product table in the AdventureWorks database and displays products that have a list price greater than or equal to $3,500.00.
Imports System Imports System.Collections.Generic Imports System.Linq Imports System.Web Imports System.Web.UI Imports System.Web.UI.WebControls Imports System.Web.UI.WebControls.Expressions Imports System.Data.Linq Partial Class CustomVB Inherits System.Web.UI.Page Protected Sub FilterProducts(ByVal sender As Object, ByVal e As CustomExpressionEventArgs) e.Query = From p In e.Query.Cast(Of Product)() _ Where p.ListPrice >= 3500 _ Select p End Sub
using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.UI; using System.Web.UI.WebControls; using System.Web.UI.WebControls.Expressions; using System.Linq; public partial class _Default : System.Web.UI.Page { protected void FilterProducts(object sender, CustomExpressionEventArgs e) { e.Query = from p in e.Query.Cast<Product>() where p.ListPrice >= 3500 select p; } }
.NET Framework
Supported in: 4Windows 7, Windows Vista SP1 or later, Windows XP SP3, 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.