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
15787	select_related with nested fields affects query result	kriomant@…	nobody	"I belive select_related should never affect query result, but only optimize referenced objects loading. However, I've found a case where query result is changed.

=== models.py ===
{{{#!python
from django.db import models

class Thing(models.Model):
	name = models.CharField(max_length=255)

	def __unicode__(self):
		return self.name

class User(models.Model):
	login = models.CharField(max_length=255)

class Lock(models.Model):
	description = models.CharField(max_length=255)

	# Only one lock per thing is allowed.
	thing = models.OneToOneField(Thing)

	user = models.ForeignKey(User)

}}}

=== tests.py ===
{{{#!python
from django.test import TestCase

from reproduce.models import *

class SimpleTest(TestCase):
	def setUp(self):
		user = User.objects.create(login='james')

		# Unlocked thing.
		self.unlocked_thing = Thing.objects.create(name='unlocked')

		# Locked thing.
		self.locked_thing = Thing.objects.create(name='locked')
		Lock.objects.create(thing=self.locked_thing, description='lock', user=user)

	def test_simple_query(self):
		things = Thing.objects.all()
		self.assertEqual(set(things), set([self.unlocked_thing, self.locked_thing]))

	def test_select_related(self):
		things = Thing.objects.select_related('lock')
		self.assertEqual(set(things), set([self.locked_thing, self.unlocked_thing]))

	def test_deep_select_related(self):
		things = Thing.objects.select_related('lock', 'lock__user')
		# This fails.
		self.assertEqual(set(things), set([self.locked_thing, self.unlocked_thing]))
}}}

''./manage.py test reproduce'' produces:

{{{
Creating test database for alias 'default'...
F..
======================================================================
FAIL: test_deep_select_related (reproduce.tests.SimpleTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File ""/home/.../select_related_bug/reproduce/tests.py"", line 27, in test_deep_select_related
    self.assertEqual(set(things), set([self.locked_thing, self.unlocked_thing]))
AssertionError: Items in the second set but not the first:
<Thing: unlocked>

----------------------------------------------------------------------
Ran 3 tests in 0.006s

FAILED (failures=1)
Destroying test database for alias 'default'...
}}}
"	Bug	closed	Database layer (models, ORM)	1.3	Normal	fixed		daniel.barreto.n@… l0ki	Accepted	0	0	0	0	0	0