Get related entity id without loading it - entity-framework

Question

I need to list all the orders with their corresponding customer ID using Entity Framework (Code First). This should be possible without querying the Customers table since the customer ID is a FK in the Orders table. However, EF generates selects against the Orders and the Customers tables as well.
This is the entities model and the code used to query Orders:
public class Order
{
public virtual Guid Id { get; set; }
public virtual string Description { get; set; }
public virtual Customer Customer { get; set; }
}
public class Customer
{
public virtual Guid Id { get; set; }
public virtual string Name { get; set; }
}
using (var context = new LazyLoadingEfContext())
{
foreach (var order in context.Orders)
{
Console.WriteLine("Order {0}, Customer {1}", order.Description, order.Customer.Id);
}
}
The SQL generated is the following:
SELECT
1 AS [C1],
[Extent1].[Id] AS [Id],
[Extent1].[Description] AS [Description],
[Extent1].[Customer_Id] AS [Customer_Id]
FROM [dbo].[Orders] AS [Extent1]
exec sp_executesql N'SELECT
[Extent2].[Id] AS [Id],
[Extent2].[Name] AS [Name]
FROM [dbo].[Orders] AS [Extent1]
INNER JOIN [dbo].[Customers] AS [Extent2] ON [Extent1].[Customer_Id] = [Extent2].[Id]
WHERE ([Extent1].[Customer_Id] IS NOT NULL) AND ([Extent1].[Id] =
#EntityKeyValue1)',N'#EntityKeyValue1 uniqueidentifier',
#EntityKeyValue1='FF947EF3-5A3F-4A26-BDB9-039C49F559A7'
(plus other identical queries with different values for the parameter #EntityKeyValue1)
Is there any way to configure EF in order to retrieve related entity IDs from the "parent" object instead of loading the related entity?
BTW, I've tested the same scenario using NHibernate and only one query is executed against the Orders table:
SELECT this_.Id as Id1_0_, this_.Description as Descript2_1_0_,
this_.Customer_id as Customer3_1_0_ FROM [Order] this_

Answer 1

Try this:
public class Order
{
public virtual Guid Id { get; set; }
public virtual string Description { get; set; }
public Guid CustomerID { get; set; }
[ForeignKey("CustomerID ")]
public virtual Customer Customer { get; set; }
}
After that you should be able to get just order.CustomerID within your foreach loop, without querying Customers table.