Add support for filterset_class meta parameter

[ghost]

This would enable filtering on Django relationships that create a default DjangoFilterConnectionField based on the model type and its meta parameters.

• Allow for use of either filter_fields or filterset_class
• Add tests to check that the behavior is similar to filter_fields
• Add documentation to show how to make use of the parameter

[coveralls]

Coverage increased (+0.02%) to 94.381% when pulling d2f8bf7 on sierreis:filterset-class into ea2cd98 on graphql-python:master.

[coveralls]

Coverage decreased (-0.06%) to 94.298% when pulling 5c191b9 on sierreis:filterset-class into ea2cd98 on graphql-python:master.

[zbyte64]

Is there a particular reason why we don't pass the provided filterset class through get_filterset_class / setup_filterset which injects GrapheneFilterSetMixin ?

[ghost]

Nope, I just pushed a fix for that part so that it has the same behavior as passing in the FilterSet as an argument to DjangoFilterConnectionField. I think there's some important overriding behavior in the mixin to work with Relay node IDs rather than the database ID.

[zbyte64]

This seems reasonable to me.

[zbyte64]

Test coverage decreased because a new scenario is not tested:

• Failure when both filter_fields & filter_class are defined

[ghost]

@mvanlonden, the latest commit should have the previously requested test case (when filter_fields and filterset_class are both set), and the coverage is now up 0.2%. Let me know if you had something else in mind.