Commit 6184cb9b authored by Ian Foote's avatar Ian Foote Committed by Simon Charette
Browse files

[1.7.x] Fixed #25693 -- Prevented data loss with Prefetch and ManyToManyField. 

Thanks to Jamie Matthews for finding and explaining the bug.

Backport of 46085737 from master
parent 85a41b44

django/db/models/query.py

+8 −0
Original line number Diff line number Diff line
@@ -1910,6 +1910,14 @@ def prefetch_one_level(instances, prefetcher, lookup, level): 
        instance_attr_val = instance_attr(obj)

        vals = rel_obj_cache.get(instance_attr_val, [])

        to_attr, as_attr = lookup.get_current_to_attr(level)



        # Check we are not shadowing a field on obj.

        if as_attr:

            for related_m2m in obj._meta.get_all_related_many_to_many_objects():

                if related_m2m.get_accessor_name() == to_attr:

                    msg = 'to_attr={} conflicts with a field on the {} model.'

                    raise ValueError(msg.format(to_attr, obj.__class__.__name__))



        if single:

            val = vals[0] if vals else None

            to_attr = to_attr if as_attr else cache_name

docs/releases/1.7.11.txt

0 → 100644
+13 −0
Original line number Diff line number Diff line 
===========================

Django 1.7.11 release notes

===========================



*Under development*



Django 1.7.11 fixes a data loss bug in 1.7.10.



Bugfixes

========



* Fixed a data loss possibility with :class:`~django.db.models.Prefetch` if

  ``to_attr`` is set to a ``ManyToManyField`` (:ticket:`25693`).

docs/releases/index.txt

+1 −0
Original line number Diff line number Diff line
@@ -25,6 +25,7 @@ versions of the documentation contain the release notes for any later releases. 
.. toctree::

   :maxdepth: 1



   1.7.11

   1.7.10

   1.7.9

   1.7.8

tests/prefetch_related/tests.py

+11 −0
Original line number Diff line number Diff line
@@ -221,6 +221,17 @@ class PrefetchRelatedTests(TestCase): 
        self.assertTrue('prefetch_related' in str(cm.exception))

        self.assertTrue("name" in str(cm.exception))



    def test_m2m_shadow(self):

        msg = 'to_attr=books conflicts with a field on the Author model.'

        poems = Book.objects.filter(title='Poems')

        with self.assertRaisesMessage(ValueError, msg):

            list(Author.objects.prefetch_related(

                Prefetch('books', queryset=poems, to_attr='books'),

            ))

        # Without the ValueError, a book was deleted due to the implicit

        # save of reverse relation assignment.

        self.assertEqual(self.author1.books.count(), 2)





class CustomPrefetchTests(TestCase):

    @classmethod