Cannot resolve keyword u'group_ptr' into field. Choices are: group, id, name, permissions, user

[Chris Chan]

I recently tried to upgrade from 1.5.1 to 1.6.2 and am now getting this error for inherited many to many relationships.

Traceback (most recent call last):

File "<stdin>", line 1, in <module>
File "/opt/bg/common/lib/python2.7/site-packages/django/db/models/manager.py", line 133, in all

return self.get_queryset()

File "/opt/bg/common/lib/python2.7/site-packages/django/db/models/fields/related.py", line 549, in get_queryset

return super(ManyRelatedManager, self).get_queryset().using(db)._next_is_sticky().filter(self.core_filters)

File "/opt/bg/common/lib/python2.7/site-packages/django/db/models/query.py", line 590, in filter

return self._filter_or_exclude(False, *args, kwargs)

File "/opt/bg/common/lib/python2.7/site-packages/django/db/models/query.py", line 608, in _filter_or_exclude

clone.query.add_q(Q(*args, kwargs))

File "/opt/bg/common/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 "/opt/bg/common/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1234, in _add_q

current_negated=current_negated)

File "/opt/bg/common/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1100, in build_filter

allow_explicit_fk=True)

File "/opt/bg/common/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1357, in setup_joins

names, opts, allow_many, allow_explicit_fk)

File "/opt/bg/common/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1277, in names_to_path

"Choices are: %s" % (name, ", ".join(available)))

django.core.exceptions.FieldError: Cannot resolve keyword u'group_ptr' into field. Choices are: group, id, name, permissions, user

[Chris Chan]

My model looks like so.

import json, logging, hashlib, random, time, base64, sys, urlparse
from django.contrib.auth.models import User as DjangoUser, Group as DjangoGroup, GroupManager as DjangoGroupManager

class GroupManager(DjangoGroupManager):

pass

class Group(DjangoGroup):

group_name = models.CharField(max_length=80, null=False)
users = models.ManyToManyField('User', through='Membership', related_name="groups")

objects = GroupManager()

def str(self):

return self.group_name

def unicode(self):

return self.str()

def save(self, *args, kwargs):

# Per django, name needs to be unique
# But in our case, different companies can have the same group name
if not self.id:

self.name = generateSalt()

super(Group, self).save(*args, kwargs)

def generateSalt():

salt = hashlib.sha1(str(random.random())).hexdigest()[:5]
t = int(time.time())
if isinstance(t, unicode):

t = t.encode('utf-8')

return hashlib.sha1(salt + str(t)).hexdigest()

class User(DjangoUser):

deleted = models.BooleanField(default=False, null=False)
active = models.BooleanField(default=True, null=False)

def str(self):

return self.getFullName()

def unicode(self):

return unicode(self.str())

class Membership(models.Model):

user = models.ForeignKey(User)
group = models.ForeignKey(Group)
date_joined = models.DateField()

[Chris Chan]

This error will happen when you try to navigate through the users' django.db.models.fields.related.ManyRelatedManager

g = Group.objects.get(id=89)
g.users.all()

[Baptiste Mispelon]

I slimmed down the models a bit:

from django.db import models

from django.contrib.auth.models import User as DjangoUser, Group as DjangoGroup

class User(DjangoUser):
    pass

class Group(DjangoGroup):
    users = models.ManyToManyField(User, through='Membership', related_name='groups')

class Membership(models.Model):
    user = models.ForeignKey(User)
    group = models.ForeignKey(Group)

The problem seems to be the related_name='groups' parameter. If you remove it, things work.

I'm not fully convinced that this is a bug because having groups as a related_name actually clashes with the groups field on User.

[AeroNotix]

​https://docs.djangoproject.com/en/dev/topics/db/models/#fields mentions that one should not create fields which clash with the API. You create a field which clashes with the API. Ergo, it doesn't work.

[chrismedrela]

@AeroNotix, you're right, but the clash should be detected by system check framework. I and mondone have written a patch: ​https://github.com/django/django/pull/2289.

[Baptiste Mispelon <bmispelon@…>]

In d0133504e57589dc8983a20bf488e069bddd772c:

Fixed #22047 -- detecting related_name clash with inheritance

Thanks to mondone for fruitful colaboration.

[Chris Chan]

Thanks for discovering the real issue, I'll ensure there are no field and related name clashes, the error didnt help much in seeing that issue.