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
8170	Managers should be inherited correctly from extended Models	Archatas	Malcolm Tredinnick	"If I have a base model which has a manager and is inherited later, all managers in the inherited model are broken.

For example, I define the {{{Vehicle}}} model which should have the default manager {{{objects}}} and also a specific manager {{{vehicles}}}. Then {{{Airplane}}} extends {{{Vehicle}}}.

{{{
# -*- coding: utf-8 -*-
from django.db import models

class VehicleManager(models.Manager):
    pass

class Vehicle(models.Model):
    title = models.CharField(max_length=255)
    pos_x = models.IntegerField()
    pos_y = models.IntegerField()
    
    objects = models.Manager()
    vehicles = VehicleManager()
    
    class Meta:
        abstract = True

class Airplane(Vehicle):
    pos_z = models.IntegerField()
}}}

When I filter out air planes now by any field from the Vehicle model, I get an error message:
{{{
>>> models.Airplane.objects.filter(pos_x=2)
  ...
  File ""C:\Python24\lib\site-packages\django\db\models\sql\query.py"", line 1238, in setup_joins
    cached_data = opts._join_cache.get(name)
AttributeError: 'Options' object has no attribute '_join_cache'
}}}

When I filter out air planes by any field from the Airplane model, I get another error message:
{{{
>>> models.Airplane.objects.filter(pos_z=2)
  ...
  File ""C:\Python24\lib\site-packages\django\db\models\sql\query.py"", line 1215, in setup_joins
    raise FieldError(""Cannot resolve keyword %r into field. ""
FieldError: Cannot resolve keyword 'pos_z' into field. Choices are: pos_x, pos_y, title
}}}

After exploring further I found out that the {{{model}}} attribute of the managers equals to {{{Vehicle}}} instead of {{{Airplane}}}. If I reassign that after model creation, then the managers work as expected:
{{{
>>> Airplane.objects.model = Airplane
>>> Airplane.vehicles.model = Airplane
>>> Airplane.objects.filter(pos_x=2)
[]
>>> Airplane.objects.filter(pos_z=2)
[]
>>> Airplane.vehicles.filter(pos_x=2)
[]
>>> Airplane.vehicles.filter(pos_z=2)
[]
}}}"		closed	Database layer (models, ORM)	dev		duplicate			Accepted	0	0	0	0	0	0