#11568: Ordering by related attributes makes distinct() break
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Reporter: sfllaw | Owner: nobody
Status: new | Milestone:
Component: Database layer (models, ORM) | Version: 1.0
Keywords: order_by distinct ForeignKey | Stage: Unreviewed
Has_patch: 0 |
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The problem is that sorting on an attribute of a related model causes
```distinct()``` to fail.
This is because the ```SELECT DISTINCT``` operates on the extra column
required for the LEFT OUTER JOIN, which makes it impossible to group the
desired results.
To reproduce the error, run this test case:
'''models.py'''
{{{
import django
from django.db import models
class Article(models.Model):
title = models.CharField(max_length=128)
def __unicode__(self):
return self.title
class Comment(models.Model):
article = models.ForeignKey(Article)
comment = models.CharField(max_length=128)
def __unicode__(self):
return "%s on %s" % (self.comment, self.article.title)
}}}
'''tests.py'''
{{{
from django.test import TestCase
from django import db
from django.conf import settings
from .models import Article, Comment
class TestOrderDistinctBug(TestCase):
def test(self):
settings.DEBUG = True
awesome = Article.objects.create(title="Awesome Title")
different = Article.objects.create(title="Different Title")
wonderfull = Article.objects.create(title="Bad Title")
Comment.objects.create(article=awesome, comment="Agreed")
Comment.objects.create(article=awesome, comment="Dummy")
Comment.objects.create(article=different, comment="Yeah")
Comment.objects.create(article=different, comment="Onoz ")
Comment.objects.create(article=wonderfull, comment="First !")
db.reset_queries()
articles = Article.objects.order_by("comment__comment").distinct()
print "articles=%s" % articles
# articles=[<Article: Awesome Title>, <Article: Awesome Title>,
<Article: Bad Title>, <Article: Different Title>, <Article: Different
Title>]
print "sql is : %s" % db.connection.queries[0]
# sql is : {'time': '0.001',
# 'sql': u'SELECT DISTINCT `order_bug_article`.`id`,
`order_bug_article`.`title`, `order_bug_comment`.`comment`
# FROM `order_bug_article` LEFT OUTER JOIN `order_bug_comment` ON
(
# `order_bug_article`.`id` = `order_bug_comment`.`article_id`
# ) ORDER BY `order_bug_comment`.`comment` ASC LIMIT 21'}
# count returns the right thing
self.assertEquals(articles.count(), 3)
# but the content of the query set is wrong
self.assertEquals(len(articles), 3)
}}}
--
Ticket URL: <http://code.djangoproject.com/ticket/11568>
Django <http://code.djangoproject.com/>
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