How to handle Foreign Keys with Entity Framework

Question

I have two entities. Groups. Pools. A Group can create many pools.

So I setup my Pool table to have a GroupID foreign key.

My code:

using (entity _db = new entity()) {
    Pool p     = new Pool();
    p.Name     = "test";
    p.Group.ID = "5";
    _db.AddToPool(p);
}

This doesn't work. I get a null reference exception on p.Group.

How do I go about creating a new "Pool" and associating a GroupID?

Answer 1

You can either load the existing Group object, say group, from your context and then set p.Group = group or with EF4 you can set the GroupID on your pool directly since it can expose the foreign key properties if you specify that in the EDMX.