Inconsistent behavior when filtering by inherited models when using a proxy model

[Luis A. Arce]

Having the following scenario:

import django.db.models  as db_models

class ParentModel(db_models.Model):
    pass

class ChildModel(ParentModel):
    pass

class ParentProxyModel(ParentModel):
    pass

    class Meta:
        proxy=True

I can filter the ParentModel in terms of existing inheriting children, but not ParentProxyModel. An example:

Python 2.7.5 (default, Jun 25 2014, 10:19:55) 
[GCC 4.8.2 20131212 (Red Hat 4.8.2-7)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)

>>> a = ParentModel.objects.create()
>>> b = ChildModel.objects.create()

>>> ParentModel.objects.filter(childmodel=None)
[<ParentModel: ParentModel object>]

>>> ParentProxyModel.objects.filter(childmodel=None)

Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/home/ajaest/Code/pfc/src/.env/lib/python2.7/site-packages/django/db/models/manager.py", line 163, in filter
    return self.get_queryset().filter(*args, **kwargs)
  File "/home/ajaest/Code/pfc/src/.env/lib/python2.7/site-packages/django/db/models/query.py", line 590, in filter
    return self._filter_or_exclude(False, *args, **kwargs)
  File "/home/ajaest/Code/pfc/src/.env/lib/python2.7/site-packages/django/db/models/query.py", line 608, in _filter_or_exclude
    clone.query.add_q(Q(*args, **kwargs))
  File "/home/ajaest/Code/pfc/src/.env/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1198, in add_q
    clause = self._add_q(where_part, used_aliases)
  File "/home/ajaest/Code/pfc/src/.env/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1234, in _add_q
    current_negated=current_negated)
  File "/home/ajaest/Code/pfc/src/.env/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1100, in build_filter
    allow_explicit_fk=True)
  File "/home/ajaest/Code/pfc/src/.env/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1357, in setup_joins
    names, opts, allow_many, allow_explicit_fk)
  File "/home/ajaest/Code/pfc/src/.env/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1277, in names_to_path
    "Choices are: %s" % (name, ", ".join(available)))
FieldError: Cannot resolve keyword 'childmodel' into field. Choices are: id, parentmodel_ptr
>>> 

[Luis A. Arce]

Maybe the problem is easy to fix. There you have a couple of examples I was able to run after a small hack:

Python 2.7.5 (default, Jun 25 2014, 10:19:55) 
[GCC 4.8.2 20131212 (Red Hat 4.8.2-7)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)

>>> ParentModel.objects.filter(childmodel=None)
[<ParentModel: ParentModel object>]

>>> ParentProxyModel.objects.filter(childmodel=None)
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/home/ajaest/Code/pfc/src/.env/lib/python2.7/site-packages/django/db/models/manager.py", line 163, in filter
    return self.get_queryset().filter(*args, **kwargs)
  File "/home/ajaest/Code/pfc/src/.env/lib/python2.7/site-packages/django/db/models/query.py", line 590, in filter
    return self._filter_or_exclude(False, *args, **kwargs)
  File "/home/ajaest/Code/pfc/src/.env/lib/python2.7/site-packages/django/db/models/query.py", line 608, in _filter_or_exclude
    clone.query.add_q(Q(*args, **kwargs))
  File "/home/ajaest/Code/pfc/src/.env/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1198, in add_q
    clause = self._add_q(where_part, used_aliases)
  File "/home/ajaest/Code/pfc/src/.env/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1234, in _add_q
    current_negated=current_negated)
  File "/home/ajaest/Code/pfc/src/.env/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1100, in build_filter
    allow_explicit_fk=True)
  File "/home/ajaest/Code/pfc/src/.env/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1357, in setup_joins
    names, opts, allow_many, allow_explicit_fk)
  File "/home/ajaest/Code/pfc/src/.env/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1277, in names_to_path
    "Choices are: %s" % (name, ", ".join(available)))
FieldError: Cannot resolve keyword 'childmodel' into field. Choices are: id

>>> qs = ParentModel.objects.filter(childmodel=None)
>>> qs.model = ParentProxyModel
>>> qs
[<ParentProxyModel: ParentProxyModel object>]
>>> 

Python 2.7.5 (default, Jun 25 2014, 10:19:55) 
[GCC 4.8.2 20131212 (Red Hat 4.8.2-7)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)

>>> ParentModel.objects.annotate(childmodel_count=Count('childmodel')).values_list('childmodel')
[(None,), (2L,)]

>>> ParentProxyModel.objects.annotate(childmodel_count=Count('childmodel')).values_list('childmodel')
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/home/ajaest/Code/pfc/src/.env/lib/python2.7/site-packages/django/db/models/manager.py", line 169, in annotate
    return self.get_queryset().annotate(*args, **kwargs)
  File "/home/ajaest/Code/pfc/src/.env/lib/python2.7/site-packages/django/db/models/query.py", line 714, in annotate
    is_summary=False)
  File "/home/ajaest/Code/pfc/src/.env/lib/python2.7/site-packages/django/db/models/sql/query.py", line 985, in add_aggregate
    field_list, opts, self.get_initial_alias())
  File "/home/ajaest/Code/pfc/src/.env/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1357, in setup_joins
    names, opts, allow_many, allow_explicit_fk)
  File "/home/ajaest/Code/pfc/src/.env/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1277, in names_to_path
    "Choices are: %s" % (name, ", ".join(available)))
FieldError: Cannot resolve keyword 'childmodel' into field. Choices are: id

>>> qs = ParentModel.objects.annotate(childmodel_count=Count('childmodel'))
>>> qs.model = ParentProxyModel
>>> qs.values_list('childmodel_count')
[(0,), (1,)]

>>> 

Both examples work even if the database was not hit (and therefore the cache not filled)

[Shai Berger]

I don't see anything "inconsistent" here -- it simply seems that proxy models do not inherit the reverse one-to-one relations added by multi-table child models.

Can you verify if they inherit other reverse relations?

Also, can you check against 1.7? Django 1.6 has entered the "critical fixes only" phase of its life.

[Tim Graham]

@ajaest, please reopen if you can follow-up to Shai's reply.