#15787: select_related with nested fields affects query result
------------------------+---------------------------------------------
Reporter: kriomant@… | Owner: nobody
Type: Bug | Status: new
Milestone: | Component: Database layer (models, ORM)
Version: 1.3 | Severity: Normal
Keywords: | Triage Stage: Unreviewed
Has patch: 0 |
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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'...
}}}
--
Ticket URL: <http://code.djangoproject.com/ticket/15787>
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