I have an AUDIO class. This audio has a SOUND_A subclass and a SOUND_B subclass. This is all done correctly and is working fine.

I have another model, lets call it PLAYLIST_JOIN, and this can contain (in the real world) SOUND_A's and SOUND_B's, so we give it a relationship of AUDIO and PLAYLIST.

This all works in the app.

The problem I am having now is querying the PLAYLIST_JOIN table with an NSPredicate. What I want to do is find an exact PLAYLIST_JOIN item by giving it 2 keys in the predicate

sound_a._sound_a_id = %@ && playlist.playlist_id = %@

and

sound_b.sound_b_id = %@ && playlist.playlist_id = %@

The main problem is that because the table does not store sound_a and sound_b, but stored audio, I cannot use this syntax. I do not have the option of reorganizing the sound_a and sound_b to use the same _id attribute name, so how do I do this?

Can I pass a method to the predicate? something like this:

[audio getID] = %@ && playlist_id = %@