Commit 5fc9a1b8 authored by Ian Foote's avatar Ian Foote Committed by Tim Graham
Browse files

[1.8.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 8c8a6d8a

django/db/models/query.py

+11 −0
Original line number Diff line number Diff line
@@ -1635,6 +1635,17 @@ 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:

            try:

                field = obj._meta.get_field(to_attr)

            except exceptions.FieldDoesNotExist:

                pass

            else:

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

                raise ValueError(msg.format(to_attr, field.model.__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/1.8.7.txt

+3 −0
Original line number Diff line number Diff line
@@ -21,3 +21,6 @@ Bugfixes 


* Fixed a regression in 1.8.6 that caused an application with South migrations

  in the ``migrations`` directory to fail (:ticket:`25618`).



* 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
@@ -39,6 +39,7 @@ 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
@@ -223,6 +223,17 @@ class PrefetchRelatedTests(TestCase): 
        self.assertIn('prefetch_related', str(cm.exception))

        self.assertIn("name", 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