Filter Templates - ASP.NET Dynamic Data - page 146

LISTING 5.5

Simple Search Page with DynamicFilter Controls (Markup)

<%@ Page Title=”” Language=”C#”
MasterPageFile=”~/Site.master” CodeBehind=”SamplePage.aspx.cs”
Inherits=”WebApplication.Samples.Ch05.DynamicFilter.SamplePage” %>

<asp:Content ContentPlaceHolderID=”main” runat=”server”>
Customer City:
<asp:DynamicFilter runat=”server” ID=”cityFilter”
DataField=”City” FilterUIHint=”Text” />
Title:
<asp:DynamicFilter runat=”server” ID=”titleFilter”
DataField=”ContactTitle” FilterUIHint=”Text” />
<asp:Button runat=”server” Text=”Find” />
<asp:GridView ID=”gridView” runat=”server” DataSourceID=”dataSource” />
<asp:EntityDataSource runat=”server” ID=”dataSource”
ConnectionString=”name=NorthwindEntities”
DefaultContainerName=”NorthwindEntities” EntitySetName=”Customers” />
<asp:QueryExtender runat=”server” TargetControlID=”dataSource”>
<asp:DynamicFilterExpression ControlID=”cityFilter” />
<asp:DynamicFilterExpression ControlID=”titleFilter” />
</asp:QueryExtender>
</asp:Content>

At run time, the new version of the page looks identical to the original shown in Figure
5.1. However, notice that the DynamicFilter controls are used instead of text boxes.
DynamicFilter is a new ASP.NET control provided by Dynamic Data. At run time, it
dynamically loads an appropriate filter template for the column specified in its DataField
property. On this page, you have two instances of the DynamicFilter control, one for the
City column and one for the ContactTitle.

Each DynamicFilter control must be ultimately connected to a LINQ-based data source
control that queries the database. In this example, Entity Framework is used, and there is
an EntityDataSource control on this page, configured to retrieve rows from the
Customers table. EntityDataSource class inherits the QueryCreated event from its base
class, QueryableDataSource . The control fires this event after it has created the initial
LINQ query, an IQueryable instance, but before the query is converted to SQL and sent to
the database server for execution. During this event, the query can be modified by the
DynamicFilter controls.

In addition to the data source control, there's also a QueryExtender control on the page.
This control is associated with a QueryableDataSource by specifying its ID in the
TargetControlID property of the query extender. At run time, the query extender handles
the QueryCreated of the data source control and passes the IQueryable instance to every
one of its data source expressions. This page uses two DynamicFilterExpression instances
to associate both of the DynamicFilter controls with the QueryExtender . Each