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How to: Load Related Data
Programmer's Guide > Quick-Start Scenarios > Silverlight > Silverlight 4 & 5 > WCF RIA Services > How to: Load Related Data

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In this walkthrough, you will learn how to add a query method in the Domain Service to return related data.

This topic is based on the WCF RIA Services example solution from the Walkthrough: Creating a RIA Services Solution.

Editing a Domain Service Query to Return Related Data

In order to return related data you should add a custom query method in the partial domain service. The process of adding query methods is explained in the Walkthrough: Adding Query Methods. The following example shows you how to return all cars bought by a specific customer.

To add a query method that accepts a parameter and returns related data:

  1. Open the solution that exposes data from the Customer table.
  2. In the server project, open the partial domain service class that exposes data from the Customer table.
  3. Add a query method that accepts a string parameter and returns all Car objects, which are bought by the Customer.
    C# Copy Code
    public partial class SofiaCarRentalDomainService
    {
           public IQueryable<Car> GetCarByCustomerName( string customerName )
       {
           var query = from c     in this.DataContext.Cars
                       from ro     in this.DataContext.RentalOrders
                       where ro.CarID == c.CarID && ro.Customer.FullName == customerName
                       select c;
               return query;
       }
    }
    VB.NET Copy Code
    Partial Public Class SofiaCarRentalDomainService
     Public Function GetCarByCustomerName(ByVal customerName As String) As IQueryable(Of Car)
      Dim query = From c In Me.DataContext.Cars, ro In Me.DataContext.RentalOrders
         Where ro.CarID = c.CarID AndAlso ro.Customer.FullName = customerName
         Select c
      Return query
     End Function
    End Class

To display the results of those query methods in the client project:

  1. In the client project, open MainPage.xaml.
  2. Add a ComboBox and a DataGrid to the user interface so that the user can filter Car records by the full name of the Customer.
  3. The following XAML shows a complete layout.
    XAML Copy Code
    <UserControl x:Class="OA.SL.RIA.Demo.MainPage"
                    xmlns:data="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Data">
           <Grid x:Name="LayoutRoot"
                 Background="White">
               <Grid.RowDefinitions>
                   <RowDefinition Height="Auto" />
                   <RowDefinition />
               </Grid.RowDefinitions>
               <ComboBox x:Name="CustomersCombo"
                         ItemsSource="{Binding}"
                         Width="200"
                         Height="30"
                         Margin="5,5,5,0"
                         HorizontalAlignment="Left"
                         DisplayMemberPath="FullName"
                         SelectionChanged="CustomersCombo_SelectionChanged"/>
               <data:DataGrid x:Name="CarsGrid"
                              Grid.Row="1" />
           </Grid>
    </    UserControl>
  4. Open the code-behind page for MainPage.xaml.
  5. Add code to retrieve query results.
    C# Copy Code
    using System.ServiceModel.DomainServices.Client;
    using System.Windows.Controls;
    using OA.SL.RIA.Demo.Web;
    using SofiaCarRentalEntityDiagramsModel;
    namespace OA.SL.RIA.Demo
    {
           public partial class MainPage : UserControl
       {
               private SofiaCarRentalDomainContext dbContext = new SofiaCarRentalDomainContext();
               public MainPage()
           {
               InitializeComponent();
               LoadOperation<Customer> loadOperation =     this.dbContext.Load( this.dbContext.GetCustomersQuery() );
                   this.DataContext = loadOperation.Entities;
           }
               private void CustomersCombo_SelectionChanged( object sender, SelectionChangedEventArgs e )
           {
                   if ( this.CustomersCombo.SelectedItem == null )
                       return;
               Customer customer =     this.CustomersCombo.SelectedItem as Customer;
               LoadOperation<Car> loadOperation =     this.dbContext.Load<Car>( this.dbContext.GetCarByCustomerNameQuery( customer.FullName ) );
                   this.CarsGrid.ItemsSource = loadOperation.Entities;
           }
       }
    }
    VB.NET Copy Code
    Imports System.ServiceModel.DomainServices.Client
    Imports OA.SL.RIA.Demo.Web
    Imports OA.SL.RIA.Demo.Web.OA.SL.RIA.Demo.Web
    Partial Public Class MainPage
        Inherits UserControl
        Private dbContext As New SofiaCarRentalDomainContext()
        Public Sub New()
            InitializeComponent()
            Dim loadOperation_Renamed As LoadOperation(Of Customer) = Me.dbContext.Load(Me.dbContext.GetCustomersQuery())
            Me.DataContext = loadOperation_Renamed.Entities
        End Sub
        Private Sub CustomersCombo_SelectionChanged(ByVal sender As Object, ByVal e As SelectionChangedEventArgs)
            If Me.CustomersCombo.SelectedItem Is Nothing Then
                Return
            End If
            Dim customer_Renamed As Customer = TryCast(Me.CustomersCombo.SelectedItem, Customer)
            Dim loadOperation_Renamed As LoadOperation(Of Car) = Me.dbContext.Load(Of Car)(Me.dbContext.GetCarByCustomerNameQuery(customer_Renamed.FullName))
            Me.CarsGrid.ItemsSource = loadOperation_Renamed.Entities
        End Sub
    End Class
  6. Run the application. The following illustration shows a list of Cars filtered by the Customer.