Imports System.Windows
Imports System.Data.Services.Client
Imports System.Collections.ObjectModel
Imports System.Collections.Specialized
Imports SilverlightClient.Northwind

Dim svcContext
Dim ordersBindingCollection
Dim detailsBindingCollection

' Create the binding collections.
ordersBindingCollection = New ObservableCollection(Of Orders)()
detailsBindingCollection = New ObservableCollection(Of Order_Details)()

Private Sub ResetBindingData()
    ' Create a new data service context.
    svcContext = _
        New NorthwindEntities(New Uri("Northwind.svc", UriKind.Relative))

    ordersBindingCollection.Clear()
    detailsBindingCollection.Clear()
End Sub
' We need to persist the result of an operation 
' to be able to invoke the dispatcher.
Private currentResult As IAsyncResult
Private Sub getCustomerOrders_Click(ByVal sender As Object, ByVal e As RoutedEventArgs)
    ' Instantiate the data service context and clear any existing bindings.
    ResetBindingData()

    ' Define the delegate to callback into the process
    Dim callback As AsyncCallback = AddressOf OnCustomerOrdersQueryComplete

    ' Define the filter condition based on the customer ID.
    Dim filterExpression = "CustomerID eq '" & Me.customerId.Text & "'"

    ' Define a query to return the specifed customer and related orders.
    Dim query As DataServiceQuery(Of Customers) = _
    svcContext.Customers() _
            .AddQueryOption("$filter", filterExpression).Expand("Orders")
    Try
        ' Begin the query execution.
        query.BeginExecute(callback, query)
    Catch ex As Exception
        messageTextBlock.Text = ex.Message
    End Try
End Sub
Private Sub OnCustomerOrdersQueryComplete(ByVal result As IAsyncResult)
    ' Persist the query result for the delegate.
    currentResult = result

    ' Use the Dispatcher to ensure that the 
    ' asynchronous call returns in the correct thread.
    Dispatcher.BeginInvoke(AddressOf QueryCompletedByDispatcher)
End Sub
Private Sub QueryCompletedByDispatcher()
    Try
        ' Get the original query back from the result.
        Dim query = CType(currentResult.AsyncState, DataServiceQuery(Of Customers))

        Dim returnedCustomer = query.EndExecute(currentResult).FirstOrDefault()

        If returnedCustomer IsNot Nothing Then

            ' Load the retuned orders into the binding collection.
            For Each order As Orders In returnedCustomer.Orders
                ordersBindingCollection.Add(order)
            Next

            ' Bind the grid control to the collection and update the layout.
            Me.ordersGrid.DataContext = ordersBindingCollection
            Me.ordersGrid.UpdateLayout()

            ' Hide the relationship property columns.
            Me.ordersGrid.Columns(8).Visibility = Visibility.Collapsed
            Me.ordersGrid.Columns(11).Visibility = Visibility.Collapsed
            Me.ordersGrid.Columns(12).Visibility = Visibility.Collapsed
        End If
    Catch ex As DataServiceQueryException
        Me.messageTextBlock.Text = String.Format("Error: {0} - {1}", _
            ex.Response.StatusCode.ToString(), ex.Response.Error.Message)
    End Try
End Sub