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How to: Load Related Entities (WCF Data Services)

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Important

WCF Data Services has been deprecated and will no longer be available for download from the Microsoft Download Center. WCF Data Services supported earlier versions of the Microsoft OData (V1-V3) protocol only and has not been under active development. OData V1-V3 has been superseded by OData V4, which is an industry standard published by OASIS and ratified by ISO. OData V4 is supported through the OData V4 compliant core libraries available at Microsoft.OData.Core. Support documentation is available at OData.Net, and the OData V4 service libraries are available at Microsoft.AspNetCore.OData.

RESTier is the successor to WCF Data Services. RESTier helps you bootstrap a standardized, queryable, HTTP-based REST interface in minutes. Like WCF Data Services before it, Restier provides simple and straightforward ways to shape queries and intercept submissions before and after they hit the database. And like Web API + OData, you still have the flexibility to add your own custom queries and actions with techniques you're already familiar with.

When you need to load associated entities in WCF Data Services, you can use the LoadProperty method on the DataServiceContext class. You can also use the Expand method on the DataServiceQuery<TElement> to require that related entities be eagerly loaded in the same query response.

The example in this topic uses the Northwind sample data service and autogenerated client data service classes. This service and the client data classes are created when you complete the WCF Data Services quickstart.

Example

The following example shows how to explicitly load the Customer that is related to each returned Orders instance.

// 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);
}

' 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

Example

The following example shows how to use the Expand method to return Order Details that belong to the Orders returned by the query.

// 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);
}

' 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

See also