Objective
In this post, I will show you how to retrieve data from related entities in WCF Data Service.
If you are new to this topic, please read Introduction to WCF Data service and ODATA before going through below article
Let us say, we want to fetch details from related entities Customers and Order.
There are two ways to fetch data from both related entities.
1. Expand
2. LoadProperty
Using LoadProperty
Program.cs
NorthwindEntities context = new NorthwindEntities(new Uri("http://localhost:61091/WcfDataService1.svc/"));
try
{
foreach (Order o in context.Orders)
{
context.LoadProperty(o, "Customer");
Console.WriteLine("Customer : {0}- Order Id: {1}", o.Customer.ContactName, o.OrderID);
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
Console.Read();
}
In above code 
So in above code load property is being used to load data from related entities. Output 
Using Expand Program.cs
DataServiceQuery<Order> query =
context.Orders.Expand("Order_Details,Customer");
try
{
foreach (Order order in query.Take(4))
{
Console.WriteLine("Customer: {0}", order.Customer.ContactName);
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)
{
Console.WriteLine(ex.Message);
}
Console.Read();
So in above code
In above code Orders relation is expanded to Order_detail and Customer.
In above code retrieving top 4th record and iterating through the records to display.
Output
How would that work with a many to many entity sets.
AssetEntity : AssetId,Name
AssetTagJoin : AssetId,TagId
TagEntity: TagId,TagName
I tried cxt.Asset.Expand(“AssetTagJoin”) – works
cxt.Asset.Expand(“AssetTagJoin”).Expand(“TagEntity”) — does not work.
cxt.Asset.Expand(“AssetTagJoin,TagEntity”) — does not work.
thank you.
Mike Apken
I’m using WCF DataServices, EF
Posted by Mike Apken | August 22, 2010, 6:45 pmHi ,
You can use the query as
DataServiceQuery query = context.AssetEntity.Expand(“AssetTagJoin,Tagentity”);
I hope above should work
Posted by Dhananjay Kumar | August 22, 2010, 6:55 pm