如何：执行异步数据服务查询（WCF 数据服务）
通过使用 WCF 数据服务 客户端库，您可同时执行客户端-服务器操作，例如执行查询和保存更改。有关详细信息，请参阅异步操作（WCF 数据服务）。
备注
对于必须在特定线程中调用回调的应用程序，必须显式封送 EndExecute 方法的执行。有关更多信息，请参见异步操作（WCF 数据服务）。
本主题中的示例使用 Northwind 示例数据服务和自动生成的客户端数据服务类。 此服务和这些客户端数据类是在完成 WCF 数据服务快速入门时创建的。
示例
下面的示例显示如何通过调用 BeginExecute 方法以启动查询来执行异步查询。 内联委托调用 EndExecute 方法以显示查询结果。
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
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);
}
}
}