How do I map a composite primary key in Entity Framework 4 code first?

Question

I'm getting to grips with EF4 code first, and liking it so far. But I'm having trouble mapping an entity to a table with a composite primary key.

The configuration I've tried looks like this:

public SubscriptionUserConfiguration()

    {
                Property(u => u.SubscriptionID).IsIdentity();
                Property(u => u.UserName).IsIdentity();
    }

Which throws this exception: Unable to infer a key for entity type 'SubscriptionUser'.

What am I missing?

Answer 1

You have two identities...

Answer 2

Solved it: I should be using HasKey, not Identity. This works:

public SubscriptionUserConfiguration()
{
     HasKey(u => u.SubscriptionID);
     HasKey(u => u.UserName);
}

Answer 3

You could also use

HasKey(u => new { u.SubscriptionID, u.UserName });

Edit:

One limitation I have found is that the following do not work:

public ProjectAssignmentConfiguration()
{
    HasKey(u => u.Employee.EmployeeId);
    HasKey(u => u.Project.ProjectId);
}

or

public ProjectAssignmentConfiguration()
{
    HasKey(u => new { u.Employee.EmployeeId, u.Project.ProjectId });
}

So how do you set up an entity where the join table has a primary key that is composed of foreign keys?

Answer 4

But how to develop relationship with multiple property (Composite field). Follwoing syntax support only one property mapping

builder.Entity() .Relationship(p => p.CostCenter) .FromProperty(c => c.ActivityCodes) .HasConstraint((p, c) => p.CostCenterId == c.CostCenterId);

repeating above line for another property , it doesn't work.