When your Django app poops out with:
'RelatedManager' object is not callable
The problem might be that you’re trying to call up related fields via a foreign key field type’s auto-generated reverse-lookup attribute — but mistakenly trying to call it as a method instead of as an attribute that holds a query set. In code terms, you put:
tracks = cd.track_set()
What you meant to do was:
tracks = cd.track_set.all()