ordering on fields which use field.source

[sehmaschine]

see #3390

Here's what I suggest:
b) if ordering_fields is __all__, keep the current behaviour (ordering on all model fields). See Notes below.
c) if ordering_fields is None, allow ordering on all serializer fields (allow field names and use field.source for the actual ordering).
d) if ordering_fields are explicitely defined, allow ordering on defined fields (allow field names and use field.source for the actual ordering).

Additional changes:
a) use serializer_class OR get_serializer_class (please note that I didn't change the error message).
b) distinguish between ordering_fields and valid_fields.
c) remove serializer method fields from valid_fields.

Notes:
a) I'm not sure about __all__ versus None, because ordering on model fields seems strange (since they are not necessarily part of the serializer). Howerver, I didn't want to change the current behaviour here.

[kevin-brown]

getattr will raise an exception (an AttributeError, usually) when the requested attribute is not found on the object. in this case, you are probably looking for something like

serializer_class = view.get_serializer_class() if hasattr(view, 'get_serializer_class) else view.serializer_class

or the rough equivalent of

serializer_class = getattr(view, 'serializer_class', None)

if serializer_class is None:
    serializer_class = view.get_serializer_class()

Then again, it may just be better to prefer view.get_serializer_class() instead of relying on the serializer_class attribute.

[kevin-brown]

Note that there are two failing tests, one of which I've addressed in my in-line comment.

[sehmaschine]

@kevin-brown thanks for checking that. unfortunately, I'm not able to run the DRF tests or provide additional tests for the new behaviour.

[tomchristie]

Appreciate the feedback & work on this, but closing as per #3390.