title: NSFetchedResultsController that contains objects from a relation
body: <p>I have a <code>NSManagedObject</code> with related objects. The relation is described by a keyPath.</p>
  
  <p>Now I want to display these related objects in a table view. Of course I could just take the <code>NSSet</code> with these objects as a data source, but I'd prefer to refetch the objects with a <code>NSFetchedResultsController</code> to benefit from its features.</p>
  
  <p>How can I create a predicate that describes these objects?</p>