Filtering Data with the QueryExtender Control

A very common task for developers who create data-driven Web pages is to filter data. This traditionally has been performed by building Where clauses in data source controls. This approach can be complicated, and in some cases the Where syntax does not let you take advantage of the full functionality of the underlying database.

To make filtering easier, a new QueryExtender control has been added in ASP.NET 4. This control can be added to EntityDataSource or LinqDataSource controls in order to filter the data returned by these controls. Because the QueryExtender control relies on LINQ, the filter is applied on the database server before the data is sent to the page, which results in very efficient operations.

The QueryExtender control supports a variety of filter options. The following sections describe these options and provide examples of how to use them.

Search

For the search option, the QueryExtender control uses provided text to find records in specified fields. In the following example, the control uses the text that is entered in the TextBoxSearch control and searches for its contents in the ProductName and Supplier.CompanyName columns in the data returned from the LinqDataSource control.

<asp:LinqDataSource ID="dataSource" runat="server"> TableName="Products">

</asp:LinqDataSource>

<asp:QueryExtender TargetControlID="dataSource" runat="server">

<asp:SearchExpression DataFields="ProductName, Supplier.CompanyName"

SearchType="StartsWith">

<asp:ControlParameter ControlID="TextBoxSearch" />

</asp:SearchExpression>

</asp:QueryExtender>

Range

The range option is similar to the search option, but specifies a pair of values to define the range. In the following example, the QueryExtender control searches the UnitPrice column in the data returned from the LinqDataSource control. The range is read from the TextBoxFrom and TextBoxTo controls on the page.

<asp:LinqDataSource ID="dataSource" runat="server"> TableName="Products">

</asp:LinqDataSource>

<asp:QueryExtender TargetControlID="dataSource" runat="server">

<asp:RangeExpression DataField="UnitPrice" MinType="Inclusive"

MaxType="Inclusive">

<asp:ControlParameter ControlID="TextBoxFrom" />

<asp:ControlParameter ControlID="TexBoxTo" />

</asp:RangeExpression>

</asp:QueryExtender>

PropertyExpression

The property expression option lets you define a comparison to a property value. If the expression evaluates to true, the data that is being examined is returned. In the following example, the QueryExtender control filters data by comparing the data in the Discontinued column to the value from the CheckBoxDiscontinued control on the page.

<asp:LinqDataSource ID="dataSource" runat="server" TableName="Products">

</asp:LinqDataSource>

<asp:QueryExtender TargetControlID="dataSource" runat="server">

<asp:PropertyExpression>

<asp:ControlParameter ControlID="CheckBoxDiscontinued" Name="Discontinued" />

</asp:PropertyExpression>

</asp:QueryExtender>

CustomExpression

Finally, you can specify a custom expression to use with the QueryExtender control. This option lets you call a function in the page that defines custom filter logic. The following example shows how to declaratively specify a custom expression in the QueryExtender control.

<asp:LinqDataSource ID="dataSource" runat="server" TableName="Products">

</asp:LinqDataSource>

<asp:QueryExtender TargetControlID="dataSource" runat="server">

<asp:CustomExpression OnQuerying="FilterProducts" />

</asp:QueryExtender>

The following example shows the custom function that is invoked by the QueryExtender control. In this case, instead of using a database query that includes a Where clause, the code uses a LINQ query to filter the data.

protected void FilterProducts(object sender, CustomExpressionEventArgs e)

{

e.Query = from p in e.Query.Cast<Product>()

where p.UnitPrice >= 10

select p;

}

These examples show only one expression being used in the QueryExtender control at a time. However, you can include multiple expressions inside the QueryExtender control.

Posted in: asp.net | Tags: asp.net asp.net 4.0 queryextender queryextender queryextender control filtering filter linqdatasource targetcontrolid searchexpression searchtype propertyexpression linq

Filtering Data with the QueryExtender Control

The QueryExtender control supports a variety of filter options. The following sections describe these options and provide examples of how to use them.

Search

<asp:LinqDataSource ID="dataSource" runat="server"> TableName="Products">

</asp:LinqDataSource>

<asp:QueryExtender TargetControlID="dataSource" runat="server">

<asp:SearchExpression DataFields="ProductName, Supplier.CompanyName"

SearchType="StartsWith">

<asp:ControlParameter ControlID="TextBoxSearch" />

</asp:SearchExpression>

</asp:QueryExtender>

Range

<asp:LinqDataSource ID="dataSource" runat="server"> TableName="Products">

</asp:LinqDataSource>

<asp:QueryExtender TargetControlID="dataSource" runat="server">

<asp:RangeExpression DataField="UnitPrice" MinType="Inclusive"

MaxType="Inclusive">

<asp:ControlParameter ControlID="TextBoxFrom" />

<asp:ControlParameter ControlID="TexBoxTo" />

</asp:RangeExpression>

</asp:QueryExtender>

PropertyExpression

<asp:LinqDataSource ID="dataSource" runat="server" TableName="Products">

</asp:LinqDataSource>

<asp:QueryExtender TargetControlID="dataSource" runat="server">

<asp:PropertyExpression>

<asp:ControlParameter ControlID="CheckBoxDiscontinued" Name="Discontinued" />

</asp:PropertyExpression>

</asp:QueryExtender>

CustomExpression

<asp:LinqDataSource ID="dataSource" runat="server" TableName="Products">

</asp:LinqDataSource>

<asp:QueryExtender TargetControlID="dataSource" runat="server">

<asp:CustomExpression OnQuerying="FilterProducts" />

</asp:QueryExtender>

protected void FilterProducts(object sender, CustomExpressionEventArgs e)

{

e.Query = from p in e.Query.Cast<Product>()

where p.UnitPrice >= 10

select p;

}

These examples show only one expression being used in the QueryExtender control at a time. However, you can include multiple expressions inside the QueryExtender control.

Posted in: asp.net | Tags: asp.net asp.net 4.0 queryextender queryextender queryextender control filtering filter linqdatasource targetcontrolid searchexpression searchtype propertyexpression linq

Some new features in Dynamic Data 4.0

Dynamic Data

Dynamic Data was introduced in the .NET Framework 3.5 SP1 release in mid-2008. This feature provides many enhancements for creating data-driven applications, including the following:

· A RAD experience for quickly building a data-driven Web site.

· Automatic validation that is based on constraints defined in the data model.

· The ability to easily change the markup that is generated for fields in the GridView and DetailsView controls by using field templates that are part of your Dynamic Data project.

Note For more information, see the Dynamic Data documentation in the MSDN Library.

For ASP.NET 4, Dynamic Data has been enhanced to give developers even more power for quickly building data-driven Web sites.

Declarative DynamicDataManager Control Syntax

The DynamicDataManager control has been enhanced so that you can configure it declaratively, as with most controls in ASP.NET, instead of only in code. The markup for the DynamicDataManager control looks like the following example:

<asp:DynamicDataManager ID="DynamicDataManager1" runat="server"

AutoLoadForeignKeys="true">

<asp:DataControlReference ControlID="GridView1" />

</DataControls>

</asp:DynamicDataManager>

<asp:GridView id="GridView1" runat="server"

</asp:GridView>

This markup enables Dynamic Data behavior for the GridView1 control that is referenced in the DataControls section of the DynamicDataManager control.

New Field Templates for URLs and E-mail Addresses

ASP.NET 4 introduces two new built-in field templates, EmailAddress.ascx and Url.ascx. These templates are used for fields that are marked as EmailAddress or Url with the DataType attribute. For EmailAddress objects, the field is displayed as a hyperlink that is created by using the mailto: protocol. When users click the link, it opens the user's e-mail client and creates a skeleton message. Objects typed as Url are displayed as ordinary hyperlinks.

The following example shows how fields would be marked.

[DataType(DataType.EmailAddress)]

public object HomeEmail { get; set; }

[DataType(DataType.Url)]

public object Website { get; set; }

Creating Links with the DynamicHyperLink Control

Dynamic Data uses the new routing feature that was added in the .NET Framework 3.5 SP1 to control the URLs that end users see when they access the Web site. The new DynamicHyperLink control makes it easy to build links to pages in a Dynamic Data site. The following example shows how to use the DynamicHyperLink control:

<asp:DynamicHyperLink ID="ListHyperLink" runat="server"

Action="List" TableName="Products">

Show all products

</asp:DynamicHyperLink>

This markup creates a link that points to the List page for the Products table based on routes that are defined in the Global.asax file. The control automatically uses the default table name that the Dynamic Data page is based on.

Support for Inheritance in the Data Model

Both the Entity Framework and LINQ to SQL support inheritance in their data models. An example of this might be a database that has an InsurancePolicy table. It might also contain CarPolicy and HousePolicy tables that have the same fields as InsurancePolicy and then add more fields. Dynamic Data has been modified to understand inherited objects in the data model and to support scaffolding for the inherited tables.

Support for Many-to-Many Relationships (Entity Framework Only)

The Entity Framework has rich support for many-to-many relationships between tables, which is implemented by exposing the relationship as a collection on an Entity object. New ManyToMany.ascx and ManyToMany_Edit.ascx field templates have been added to provide support for displaying and editing data that is involved in many-to-many relationships.

New Attributes to Control Display and Support Enumerations

The DisplayAttribute has been added to give you additional control over how fields are displayed. The DisplayName attribute in earlier versions of Dynamic Data allowed you to change the name that is used as a caption for a field. The new DisplayAttribute class lets you specify more options for displaying a field, such as the order in which a field is displayed and whether a field will be used as a filter. The attribute also provides independent control of the name used for the labels in a GridView control, the name used in a DetailsView control, the help text for the field, and the watermark used for the field (if the field accepts text input).

The EnumDataTypeAttribute class has been added to let you map fields to enumerations. When you apply this attribute to a field, you specify an enumeration type. Dynamic Data uses the new Enumeration.ascx field template to create UI for displaying and editing enumeration values. The template maps the values from the database to the names in the enumeration.

Enhanced Support for Filters

Dynamic Data 1.0 shipped with built-in filters for Boolean columns and foreign-key columns. The filters did not allow you to specify whether they were displayed up or in what order they were displayed. The new DisplayAttribute attribute addresses both of these issues by giving you control over whether a column shows up as a filter and in what order it will be displayed.

An additional enhancement is that filtering support has been rewritten to use the new QueryExtender feature of Web Forms. This lets you create filters without requiring knowledge of the data source control that the filters will be used with. Along with these extensions, filters have also been turned into template controls, which allows you to add new ones. Finally, the DisplayAttribute class mentioned earlier allows the default filter to be overridden, in the same way that UIHint allows the default field template for a column to be overridden.