Commit 1252b778 authored by valtron's avatar valtron Committed by Loic Bistuer
Browse files

[1.6.x] Fixed #21760 -- prefetch_related used an inefficient query for reverse FK. 

Regression introduced by commit 97774429. Refs #21410.

Conflicts:
	tests/prefetch_related/tests.py

Backport of d3b71b97 from master
parent a3570798

AUTHORS

+1 −0
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@@ -599,6 +599,7 @@ answer newbie questions, and generally made Django that much better: 
    David Tulig <david.tulig@gmail.com>

    Justine Tunney <jtunney@lobstertech.com>

    Amit Upadhyay <http://www.amitu.com/blog/>

    valtron

    Adam Vandenberg

    Geert Vanderkelen

    Vasil Vangelovski

django/db/models/fields/related.py

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@@ -279,7 +279,9 @@ class ReverseSingleRelatedObjectDescriptor(six.with_metaclass(RenameRelatedObjec 
        # composite fields. In the meantime we take this practical approach to

        # solve a regression on 1.6 when the reverse manager in hidden

        # (related_name ends with a '+'). Refs #21410.

        if self.field.rel.is_hidden():

        # The check for len(...) == 1 is a special case that allows the query

        # to be join-less and smaller. Refs #21760.

        if self.field.rel.is_hidden() or len(self.field.foreign_related_fields) == 1:

            query = {'%s__in' % related_field.name: set(instance_attr(inst)[0] for inst in instances)}

        else:

            query = {'%s__in' % self.field.related_query_name(): instances}

docs/releases/1.6.3.txt

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@@ -67,5 +67,9 @@ Other bugfixes and changes 
* Fixed :djadmin:`changepassword` on Windows

  (`#22364 <https://code.djangoproject.com/ticket/22364>`_).



* Fixed regression in ``prefetch_related`` that caused the related objects

  query to include an unnecessary join

  (`#21760 <https://code.djangoproject.com/ticket/21760>`_).



Additionally, Django's vendored version of six, :mod:`django.utils.six` has been

upgraded to the latest release (1.6.1).

tests/prefetch_related/tests.py

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@@ -2,9 +2,11 @@ from __future__ import absolute_import, unicode_literals 


from django.contrib.contenttypes.models import ContentType

from django.db import connection

from django.db.models.query import get_prefetcher

from django.test import TestCase

from django.test.utils import override_settings

from django.utils import six

from django.utils.encoding import force_text



from .models import (Author, Book, Reader, Qualification, Teacher, Department,

    TaggedItem, Bookmark, AuthorAddress, FavoriteAuthors, AuthorWithAge,
@@ -677,3 +679,18 @@ class Ticket21410Tests(TestCase): 


    def test_bug(self):

        list(Author2.objects.prefetch_related('first_book', 'favorite_books'))





class Ticket21760Tests(TestCase):



    def setUp(self):

        self.rooms = []

        for _ in range(3):

            house = House.objects.create()

            for _ in range(3):

                self.rooms.append(Room.objects.create(house = house))



    def test_bug(self):

        prefetcher = get_prefetcher(self.rooms[0], 'house')[0]

        queryset = prefetcher.get_prefetch_queryset(list(Room.objects.all()))[0]

        self.assertNotIn(' JOIN ', force_text(queryset.query))