How to best assign object relationships in LinqToSql

Lets assume the simple case, a simple relationship between table A and table B, where B has开发者_C百科 an A_Id field in it.

Now, assume I have an object of type A (currentA), and am creating a brand new B object.

B newB = new B() { A_id = currentA.Id };

Is this the correct way to set that relationship? Or should I do:

B newB = new B() { A = currentA };

In the second case, does B.A_Id get set automatically?

Perhaps I need to explicitly set both?

B newB = new B() { A = currentA, A_Id = currentA.Id };

I am looking for the most elegant way to set this new relationship such that I can correctly save it to the database later, and can exploit it immediately... for example I might want to do:

MessageBox(String.Format("B's parent is now {0}", B.A.Name));

It was not intuitive to me at first, but the answer is to:

currentA.Bs.Add(new B());

It seems that if you Add an object to an EntitySet, it will take care of assigning the appropriate relationship properties on the Added object.