`Manager.get_empty_query_set` should call `get_query_set`

[Simon Charette]

Now that EmptyQuerySet has been removed calling none() on a QuerySet subclass returns an instance that subclass:

>>> class MyQuerySet(models.query.QuerySet): pass
>>> isinstance(MyQuerySet(MyModel).none(), MyQuerySet)
>>> True # On django >= 1.6

This is quite useful and less error prone.

However, when one subclass models.Manager to return a QuerySet subclass they must override both get_empty_query_set and get_query_set to have consistent behavior.

class MyManager(models.Manager):
    def get_query_set(self):
        return MyQuerySet(self.model, using=self._db)


class MyModel(models.Model):
    objects = MyManager()


>>> isinstance(MyModel.objects.none(), MyQuerySet) # Manager.none() calls get_empty_query_set under the hood
>>> False
>>> isinstance(MyModel.objects.all().none(), MyQuerySet)
>>> True

Another alternative (better IMHO) is to completely remove get_empty_query_set since it's not documented and only used by Manager.none and EmptyManager.get_query_set. We could make Manager.none proxy QuerySet.none and EmptyManager.get_query_set returns QuerySet.get_query_self(self).none().

Attaching two patches that both pass all tests on Python 2.7.3 SQlite.

[Anssi Kääriäinen]

Looks good to me. Marking as ready for checkin, I like the full removal approach more, it looks like it will not be needed any more.

[Anssi Kääriäinen]

Anybody know of any real use cases get_empty_query_set()? If not, I will go with the remove get_empty_query_set() approach.

I will commit this in a day or two if nobody objects...

[Simon Charette]

Looks like get_empty_query_set was introduced at the ​same time as EmptyQuerySet.

[Simon Charette <charette.s@…>]

In fb606e10ac07af6014cae838c21bf30cf50e8b40:

Fixed #19653 -- Removed Manager.get_empty_query_set.