Core Data - 'calculated' attributes

Question

I have two entities: A and B

A has two properties from and to, both pointing to the B entity. B as a fetched property to A with predicate from == $FETCH_SOURCE or to = $FETCH_SOURCE

   -- (from) ->
A  --  (to)  ->  B
   <-  (As)  --

In my application I select a certain B instance, and then show all of its A instances.

Now, in my table the columns are bound to an array controller containing the selected A instances. I want to 'merge' the from and to columns. I already know one of the columns will be equal to the selected B instance, so now I'm only interested in the second value.

The options I see:

• create a custom class for the B entity and create a method that returns either value. It should somehow be able to retrieve which B instance is currently selected.
• create a custom DataSource. Most columns are still using bindings, so then we'd have to access the NSArrayController's array so we're sure we have the right object.
• create a custom DataSource, remove the NSArrayController and do all the Core Data stuff ourselves.

Is there any 'right' way to solve this?