Composite primary keys which are also foreign keys in Entity Framework - entity-framework

Question

If I have 2 tables 1 with a composite primary key where one of the keys is also a foreign key in another table:
Table 1:
A (PK, FK - maps to X in Table 2)
B (PK)
C
Table 2:
X (PK)
Y
Because A is both the PK in table 1 and FK in table 2, when I use EF to generate the entity model, I have both a Scalar AND a Navigation property for A in table 1. I cannot seem to remove A as a scalar (I think because it is a primary key).
The problem I am having is that if I create a table1Entity and set A's scalar property to a new value, A's navigation property will not be changed automatically (and vice versa).
Ideally I just want A to expose the navigation property - which is the way it behaves if A was not also part of the composite primary key anyway. Is there any way to achieve this?

Answer 1

Am I correct in assuming that Table1 derives from Table2? If so, I would do it like so:
(I'd also change the PK for both tables to the same name, since they probably have the same meaning - for the instance of this, I'll use the example ID)
First, create the model with the default relationships (I usually just import the two tables from the database)
In the designer, right click the base type, add inheritance, select the derived type.
Delete the one to zero or one association
Then, since the base type already has column ID, delete it from the derived type.
Go to table mapping for the derived type, and map the ID property to the ID of the table.

Answer 2

Well, not really. Create the view with schemabinding and create a clustered index on the view (SQL Server 2008 or later, earlier versions I'm not sure can do that). The clustered index will be recognised as a primary key, thus tricking EF(VS) into believing the view is a real table.

Answer 3

Have you expicity set the Ids of the composite key and referenced these in your configuration?
i.e
public class Table1
{
public Table2 A{get;set}
public int AId {get;set;}
public int BId {get;set;}
}
I assume you'll need something like:
HasKey(pc => new { pc.AId, pc.BId});
HasRequired(x => x.A).WithMany().HasForeignKey(x => x.AId);

Answer 4

Instead of mapping to table 1 directly, add a view to your database that's got all of table 1's fields, plus an extra copy of A (A2).
Then, map the scalar key to A2 and the nav key to A.
(You'll run into a problem where if you use a view, Visual Studio can't find a primary key; fix this by manually editing the XML of the edmx file and adding a <Key><PropertyRef ... /></Key> to the <EntityType> for table A)
I know - it's hacky and horrible... but hey - it works!