DataServiceContext.EndExecute(IAsyncResult) Method

Definition

public System.Collections.Generic.IEnumerable<TElement> EndExecute<TElement> (IAsyncResult asyncResult);
Type Parameters
TElement

The type returned by the query.

Parameters
asyncResult
IAsyncResult

IAsyncResult object.

Returns
IEnumerable<TElement>

The results returned by the query operation.

Exceptions

When asyncResult is null.

When asyncResult did not originate from this DataServiceContext instance.

-or-

When the EndExecute<TElement>(IAsyncResult) method was previously called.

When an error is raised either during execution of the request or when it converts the contents of the response message into objects.

Examples

The following example shows how to execute an asynchronous query by calling the BeginExecute method to start the query. The inline delegate calls the EndExecute method to display the query results. This example uses the DataServiceContext generated by the Add Service Reference tool based on the Northwind data service, which is created when you complete the WCF Data Services .

public static void BeginExecuteCustomersQuery()
{
    // Create the DataServiceContext using the service URI.
    NorthwindEntities context = new NorthwindEntities(svcUri);

    // Define the query to execute asynchronously that returns 
    // all customers with their respective orders.
    DataServiceQuery<Customer> query = (DataServiceQuery<Customer>)(from cust in context.Customers.Expand("Orders")
                                       where cust.CustomerID == "ALFKI"
                                       select cust);

    try
    {
        // Begin query execution, supplying a method to handle the response
        // and the original query object to maintain state in the callback.
        query.BeginExecute(OnCustomersQueryComplete, query);
    }
    catch (DataServiceQueryException ex)
    {
        throw new ApplicationException(
            "An error occurred during query execution.", ex);
    }
}

// Handle the query callback.
private static void OnCustomersQueryComplete(IAsyncResult result)
{
    // Get the original query from the result.
    DataServiceQuery<Customer> query = 
        result as DataServiceQuery<Customer>;

    foreach (Customer customer in query.EndExecute(result))
    {
        Console.WriteLine("Customer Name: {0}", customer.CompanyName);
        foreach (Order order in customer.Orders)
        {
            Console.WriteLine("Order #: {0} - Freight $: {1}",
                order.OrderID, order.Freight);
        }
    }
}    
Public Shared Sub BeginExecuteCustomersQuery()
    ' Create the DataServiceContext using the service URI.
    Dim context = New NorthwindEntities(svcUri)

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

    ' Define the query to execute asynchronously that returns 
    ' all customers with their respective orders.
    Dim query As DataServiceQuery(Of Customer) = _
    context.Customers.Expand("Orders")

    Try
        ' Begin query execution, supplying a method to handle the response
        ' and the original query object to maintain state in the callback.
        query.BeginExecute(callback, query)
    Catch ex As DataServiceQueryException
        Throw New ApplicationException( _
                "An error occurred during query execution.", ex)
    End Try
End Sub
' Handle the query callback.
Private Shared Sub OnCustomersQueryComplete(ByVal result As IAsyncResult)
    ' Get the original query from the result.
    Dim query As DataServiceQuery(Of Customer) = _
        CType(result.AsyncState, DataServiceQuery(Of Customer))

    ' Complete the query execution.
    For Each customer As Customer In query.EndExecute(result)
        Console.WriteLine("Customer Name: {0}", customer.CompanyName)
        For Each order As Order In customer.Orders
            Console.WriteLine("Order #: {0} - Freight $: {1}", _
                    order.OrderID, order.Freight)
        Next
    Next
End Sub

Remarks

According to the standard begin-end asynchronous pattern, the provided callback is invoked when query results are retrieved. For more information, see Asynchronous Operations.

When the callback is invoked, all results have been read from the HTTP stream, but they have not been processed; no local user-facing objects have been materialized or modified and identity resolution has not occurred. When EndExecute is invoked, a DataServiceResponse is created and returned but the results still have not been processed. Identity resolution, object materialization, and manipulation occur only when the user enumerates the results.

Applies to