HOW TO：載入相關實體 (WCF Data Services)

當您需要在 WCF Data Services 中載入相關的實體時，可以在 DataServiceContext 類別上使用 LoadProperty 方法。 您也可以在 DataServiceQuery<TElement> 使用 Expand 方法，要求立即將相關實體載入至同一個查詢回應中。

本主題的範例使用 Northwind 範例資料服務，以及自動產生的用戶端資料服務類別。 此服務和用戶端資料類別會在您完成 WCF Data Services 快速入門時建立。

範例

下列範例示範如何明確地載入與所傳回之每個 Orders 執行個體相關的 Customer。

' Create the DataServiceContext using the service URI.
Dim context = New NorthwindEntities(svcUri)

Try
    ' Enumerate over the top 10 orders obtained from the context.
    For Each order As Order In context.Orders.Take(10)
        ' Explicitly load the customer for each order.
        context.LoadProperty(order, "Customer")

        ' Write out customer and order information.
        Console.WriteLine("Customer: {0} - Order ID: {1}", _
                order.Customer.CompanyName, order.OrderID)
    Next
Catch ex As DataServiceQueryException
    Throw New ApplicationException( _
            "An error occurred during query execution.", ex)
End Try

// Create the DataServiceContext using the service URI.
NorthwindEntities context = new NorthwindEntities(svcUri);

try
{
    // Enumerate over the top 10 orders obtained from the context.
    foreach (Order order in context.Orders.Take(10))
    {
        // Explicitly load the customer for each order.
        context.LoadProperty(order, "Customer");

        // Write out customer and order information.
        Console.WriteLine("Customer: {0} - Order ID: {1}", 
            order.Customer.CompanyName, order.OrderID);
    }
}
catch (DataServiceQueryException ex)
{
    throw new ApplicationException(
        "An error occurred during query execution.", ex);
}

下列範例示範如何使用 Expand 方法傳回屬於查詢所傳回之 Orders 的 Order Details 方法。

' Create the DataServiceContext using the service URI.
Dim context = New NorthwindEntities(svcUri)

' Define a query for orders that also returns items and customers.
Dim query As DataServiceQuery(Of Order) = _
context.Orders.Expand("Order_Details,Customer")

Try
    ' Enumerate over the first 10 results of the query.
    For Each order As Order In query.Take(10)
        Console.WriteLine("Customer: {0}", order.Customer.CompanyName)
        Console.WriteLine("Order ID: {0}", order.OrderID)

        For Each item As Order_Detail In order.Order_Details
            Console.WriteLine(vbTab & "Product: {0} - Quantity: {1}", _
                    item.ProductID, item.Quantity)
        Next
    Next
Catch ex As DataServiceQueryException
    Throw New ApplicationException( _
            "An error occurred during query execution.", ex)
End Try

// Create the DataServiceContext using the service URI.
NorthwindEntities context = new NorthwindEntities(svcUri);

// Define a query for orders that also returns items and customers.
DataServiceQuery<Order> query =
    context.Orders.Expand("Order_Details,Customer");

try
{
    // Enumerate over the first 10 results of the query.
    foreach (Order order in query.Take(10))
    {
        Console.WriteLine("Customer: {0}", order.Customer.CompanyName);
        Console.WriteLine("Order ID: {0}", order.OrderID);

        foreach (Order_Detail item in order.Order_Details)
        {
            Console.WriteLine("\tProduct: {0} - Quantity: {1}",
                item.ProductID, item.Quantity);
        }
    }
}
catch (DataServiceQueryException ex)
{
    throw new ApplicationException(
        "An error occurred during query execution.", ex);
}

請參閱

概念

查詢資料服務 (WCF Data Services)