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
24936	AttributeError appears when one tries to use defer/only for a field in a model that has the reverse relationship explicitly removed	lukawoj	nobody	"While investigating #24612 I discovered that if one tries to use defer/only for a field in a model that has the reverse relationship explicitly removed, AttributeError appears. Code changed since #24612 was logged and now it throws following error:
{{{
AttributeError: 'ManyToOneRel' object has no attribute 'attname'
}}}

Models:
{{{
#!python
# models.py
from django.db import models
from django.contrib.auth.models import User

class Message(models.Model):
        content = models.CharField(max_length=10)

class MessageParticipant(models.Model):
        msg = models.ForeignKey(Message, related_name='participants')
        user = models.ForeignKey(User, related_name='+')
}}}

Query to use:
{{{
list(Message.objects.all().only('participants__user__username'))
}}}

Error:
{{{
Traceback (most recent call last):
  File ""C:/dev/django_con/django_sprint_2015/django_sprint/django/tests\defer\tests.py"", line 279, in test_defer_only
    list(Message.objects.all().only('participants__user__username'))
  File ""C:\dev\django_con\django_sprint_2015\django_sprint\django\django\db\models\query.py"", line 258, in __iter__
    self._fetch_all()
  File ""C:\dev\django_con\django_sprint_2015\django_sprint\django\django\db\models\query.py"", line 1063, in _fetch_all
    self._result_cache = list(self.iterator())
  File ""C:\dev\django_con\django_sprint_2015\django_sprint\django\django\db\models\query.py"", line 52, in __iter__
    results = compiler.execute_sql()
  File ""C:\dev\django_con\django_sprint_2015\django_sprint\django\django\db\models\sql\compiler.py"", line 835, in execute_sql
    sql, params = self.as_sql()
  File ""C:\dev\django_con\django_sprint_2015\django_sprint\django\django\db\models\sql\compiler.py"", line 384, in as_sql
    extra_select, order_by, group_by = self.pre_sql_setup()
  File ""C:\dev\django_con\django_sprint_2015\django_sprint\django\django\db\models\sql\compiler.py"", line 48, in pre_sql_setup
    self.setup_query()
  File ""C:\dev\django_con\django_sprint_2015\django_sprint\django\django\db\models\sql\compiler.py"", line 39, in setup_query
    self.select, self.klass_info, self.annotation_col_map = self.get_select()
  File ""C:\dev\django_con\django_sprint_2015\django_sprint\django\django\db\models\sql\compiler.py"", line 196, in get_select
    for c in self.get_default_columns():
  File ""C:\dev\django_con\django_sprint_2015\django_sprint\django\django\db\models\sql\compiler.py"", line 504, in get_default_columns
    only_load = self.deferred_to_columns()
  File ""C:\dev\django_con\django_sprint_2015\django_sprint\django\django\db\models\sql\compiler.py"", line 772, in deferred_to_columns
    self.query.deferred_to_data(columns, self.query.get_loaded_field_names_cb)
  File ""C:\dev\django_con\django_sprint_2015\django_sprint\django\django\db\models\sql\query.py"", line 684, in deferred_to_data
    callback(target, model, values)
  File ""C:\dev\django_con\django_sprint_2015\django_sprint\django\django\db\models\sql\query.py"", line 1804, in get_loaded_field_names_cb
    target[model] = {f.attname for f in fields}
  File ""C:\dev\django_con\django_sprint_2015\django_sprint\django\django\db\models\sql\query.py"", line 1804, in <setcomp>
    target[model] = {f.attname for f in fields}
AttributeError: 'ManyToOneRel' object has no attribute 'attname'
}}}"	Bug	closed	Database layer (models, ORM)	dev	Normal	needsinfo			Unreviewed	0	0	0	0	0	0