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CustomExpression Class

Provides a way to specify a custom LINQ query that is called in response to an event.

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

public class CustomExpression : ParameterDataSourceExpression

The CustomExpression type exposes the following members.

  NameDescription
Public methodCustomExpressionInitializes a new instance of the CustomExpression class.
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  NameDescription
Protected propertyContextGets the HttpContext instance of the owner control. (Inherited from DataSourceExpression.)
Public propertyDataSourceGets the data source object that is associated with the owner control. (Inherited from DataSourceExpression.)
Protected propertyIsTrackingViewStateGets a value that indicates whether a data source expression object is tracking its view state changes. (Inherited from DataSourceExpression.)
Protected propertyOwnerGets the owner control. (Inherited from DataSourceExpression.)
Public propertyParametersGets the parameters that are associated with this DataSourceExpression object. (Inherited from ParameterDataSourceExpression.)
Protected propertyViewStateGets an instance of the StateBag class that contains the current view state information. (Inherited from DataSourceExpression.)
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  NameDescription
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.)
Public methodGetHashCodeServes as the default hash function. (Inherited from Object.)
Public methodGetQueryableProvides access to the modified IQueryable object that the data source uses. (Overrides DataSourceExpression.GetQueryable(IQueryable).)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodLoadViewStateLoads the state of the values in the ParameterDataSourceExpression object that must be persisted. (Inherited from ParameterDataSourceExpression.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Protected methodSaveViewStateSaves the current view state of the ParameterDataSourceExpression object. (Inherited from ParameterDataSourceExpression.)
Public methodSetContextExecutes the expression by using the specified owner control, context, and data source. (Inherited from ParameterDataSourceExpression.)
Public methodSetDirtyMarks the DataSourceExpression object so that its state will be saved in view state. (Inherited from DataSourceExpression.)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
Protected methodTrackViewStateTracks 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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  NameDescription
Public eventQueryingOccurs when the IQueryable data source value is set.
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  NameDescription
Explicit interface implemetationPrivate propertyIStateManager.IsTrackingViewStateWhen implemented by a class, gets a value that indicates whether a data source expression object is tracking its view state changes. (Inherited from DataSourceExpression.)
Explicit interface implemetationPrivate methodIStateManager.LoadViewStateWhen implemented by a class, loads the previously saved view state of the data source expression object. (Inherited from DataSourceExpression.)
Explicit interface implemetationPrivate methodIStateManager.SaveViewStateWhen implemented by a class, saves the current view state of the DataSourceExpression object. (Inherited from DataSourceExpression.)
Explicit interface implemetationPrivate methodIStateManager.TrackViewStateWhen 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.)
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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.

NoteNote

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.

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: 4.6, 4.5, 4

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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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