Add the ability to apply a filter to each query
Add the ability to apply a filter to each query

Usecase: want to filter each queryset to a specific user_id. We
don't have the user on hand at the time of view creation, so we
need to pass in a function to do the filtering dynamically
at runtime.

Axiologue/DjangoRestMultipleModels,pombredanne/DjangoRestMultipleModels