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
11568	Ordering by related attributes makes distinct() break	Simon Law	nobody	"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)
}}}"		closed	Database layer (models, ORM)	1.0		invalid	order_by distinct ForeignKey	benoit@… simon@…	Unreviewed	0	0	0	0	0	0