Allow DjangoObjectPermissions to use views that define get_queryset

[ticosax]

Same as #2863 but for DjangoObjectPermissions.

[xordoquy]

Looks good to me too.

[jpadilla]

Shouldn't this instead behave like has_permission?

try:
    queryset = view.get_queryset()
except AttributeError:
    queryset = getattr(view, 'queryset', None)
except AssertionError:
    # view.get_queryset() didn't find .queryset
    queryset = None

I think there's also some docs that need to be updated.

[ticosax]

There is no use case for DjangoObjectPermissions that doesn't support .queryset or .get_queryest(). Like it is today, DjangoObjectPermissions does not support queyset is None. So I think it should stay like that.
Regarding the documentation, I will update it tomorrow.
Thank you for the feedback.

[tomchristie]

Should we also fallback to view.queryset.model? That'd be consistent with the documentation above, and would be less likely to introduce any breakage to existing APIs.

Also then more consistent with #2863.

[tomchristie]

One inline comment. Once that's addressed I'm happy with this.

[ticosax]

the default implementation of .get_queryset() already serves .queryset
https://github.com/tomchristie/django-rest-framework/blob/master/rest_framework/generics.py#L47

This is why I think we do not need to fallback on view.queryset.

Therefore, for sake of consistency, I will do it the same way, by asserting the queryset exists, like it is done for DjangoModelPermissions https://github.com/tomchristie/django-rest-framework/blob/master/rest_framework/permissions.py#L123

[ticosax]

I will re-open later . I need to work on this branch a bit more.