id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
10953	Proxy model of a proxy model is of incorrect type.	Tai Lee	Jacob	"If you proxy a model that is already a proxy, it will be of the same type as the first proxy. If the second proxy is used in a foreign key, you will not be able to create any model objects which have a value for that foreign key because they will fail the type check validation.

This means we can only ever proxy actual models, and cannot create a base proxy model to subclass as necessary.

{{{
# models.

from django.contrib.auth import models as auth_models
from django.db import models

class User1(auth_models.User):
	class Meta:
		proxy = True

class User2(User1):
	class Meta:
		proxy = True

class Something(models.Model):
	user = models.ForeignKey(User2)

# interactive shell.

>>> from myapp.models import User1, User2, Something

>>> type(User1.objects.get(username='admin'))
<class 'myapp.models.User1'>

>>> type(User2.objects.get(username='admin'))
<class 'myapp.models.User1'>

>>> Something.objects.create(user=User2.objects.get(username='admin'))
Traceback (most recent call last):
  File ""<console>"", line 1, in ?
  File ""/path/to/django/db/models/manager.py"", line 126, in create
    return self.get_query_set().create(**kwargs)
  File ""/path/to/django/db/models/query.py"", line 283, in create
    obj = self.model(**kwargs)
  File ""/path/to/django/db/models/base.py"", line 308, in __init__
    setattr(self, field.name, rel_obj)
  File ""/path/to/django/db/models/fields/related.py"", line 270, in __set__
    raise ValueError('Cannot assign ""%r"": ""%s.%s"" must be a ""%s"" instance.' %
ValueError: Cannot assign ""<User1: admin>"": ""Something.user"" must be a ""User2"" instance.
}}}
"		closed	Database layer (models, ORM)	dev		fixed	proxy type foreign key		Accepted	1	0	0	0	0	0