.values()/.values_list() fails on EmptyQuerySet

[Davide Rizzo <mail@…>]

Calling .values() or .values_list() on an EmptyQuerySet raises an exception.

>>> EmptyQuerySet().values('id')
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "C:\Python27\lib\site-packages\django\db\models\query.py", line 515, in values
    return self._clone(klass=ValuesQuerySet, setup=True, _fields=fields)
  File "C:\Python27\lib\site-packages\django\db\models\query.py", line 1049, in _clone
    c = super(EmptyQuerySet, self)._clone(klass, setup=setup, **kwargs)
  File "C:\Python27\lib\site-packages\django\db\models\query.py", line 772, in _clone
    c._setup_query()
  File "C:\Python27\lib\site-packages\django\db\models\query.py", line 895, in _setup_query
    self.query.add_fields(self.field_names, False)
  File "C:\Python27\lib\site-packages\django\db\models\sql\query.py", line 1549, in add_fields
    alias = self.get_initial_alias()
  File "C:\Python27\lib\site-packages\django\db\models\sql\query.py", line 798, in get_initial_alias
    alias = self.join((None, self.model._meta.db_table, None, None))
AttributeError: 'NoneType' object has no attribute '_meta'

>>> EmptyQuerySet().values_list('id')
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "C:\Python27\lib\site-packages\django\db\models\query.py", line 525, in values_list
    _fields=fields)
  File "C:\Python27\lib\site-packages\django\db\models\query.py", line 1049, in _clone
    c = super(EmptyQuerySet, self)._clone(klass, setup=setup, **kwargs)
  File "C:\Python27\lib\site-packages\django\db\models\query.py", line 772, in _clone
    c._setup_query()
  File "C:\Python27\lib\site-packages\django\db\models\query.py", line 895, in _setup_query
    self.query.add_fields(self.field_names, False)
  File "C:\Python27\lib\site-packages\django\db\models\sql\query.py", line 1549, in add_fields
    alias = self.get_initial_alias()
  File "C:\Python27\lib\site-packages\django\db\models\sql\query.py", line 798, in get_initial_alias
    alias = self.join((None, self.model._meta.db_table, None, None))
AttributeError: 'NoneType' object has no attribute '_meta'

This seems related to #7235. I can reproduce the bug on 1.2.4 and 1.2.5 but not on 1.2.3.

### Django 1.2.3
>>> q = EmptyQuerySet()
>>> q.values_list('id')
[]

[Victor van den Elzen <victor.van.den.elzen@…>]

Like #7235, on the one hand, you shouldn't really use EmptyQuerySet without an associated model.

TestModel.objects.none().values('id')

works fine.

On the other hand we could just fix it. Patch attached.

[Davide Rizzo <mail@…>]

There is at least one real world use case that looks legit to me:

# user can be an instance of django.contrib.auth.AnonymousUser
user.groups.all().values_list('id', flat=True)

The patch works fine.

[Malcolm Tredinnick]

I'm not happy with this patch: it's returning the wrong type. The values() and values_list() calls return particular types that, when converted to a list, for example, are lists of dictionaries or lists of tuples. The EmptyQuerySet interface doesn't meet that.

Duck typing implies that if it looks like the result of a values() call, it should behave like one in all pertinent respects.

[Anssi Kääriäinen <akaariai@…>]

In 69a46c5ca7d4e6819096af88cd8d51174efd46df:

Tests for various emptyqs tickets

The tickets are either about different signature between qs.none() and
qs or problems with subclass types (either EmptyQS overrided the custom
qs class, or EmptyQS was overridden by another class - values() did
this).

Fixed #15959, fixed #17271, fixed #17712, fixed #19426