Regression from f51c1f59 with select_related + prefetch_related

[Aymeric Augustin]

If a queryset does:

• select_related through a reverse one-to-one
• prefetch_related through that one-to-one then another relation

and some objects don't have a related object through the reverse one-to-one, iterating the queryset raises an exception.

This is easier to demonstrate with a test case:

tests/prefetch_related/models.py

@@ -66 +66 @@
         AuthorWithAge, related_name='books_with_year')
 
 
+class Bio(models.Model):
+    author = models.OneToOneField(Author)
+    books = models.ManyToManyField(Book, blank=True)
+
+
 @python_2_unicode_compatible
 class Reader(models.Model):
     name = models.CharField(max_length=50)

tests/prefetch_related/tests.py

@@ -9 +9 @@
 from django.utils import six
 from django.utils.encoding import force_text
 
-from .models import (Author, Book, Reader, Qualification, Teacher, Department,
+from .models import (Author, Bio, Book, Reader, Qualification, Teacher, Department,
     TaggedItem, Bookmark, AuthorAddress, FavoriteAuthors, AuthorWithAge,
     BookWithYear, BookReview, Person, House, Room, Employee, Comment,
     LessonEntry, WordEntry, Author2)
@@ -192 +192 @@
                                      ["Amy"],
                                      ["Amy", "Belinda"]])
 
+    def test_reverse_one_to_one_then_m2m(self):
+        list(Author.objects.prefetch_related('bio__books').select_related('bio'))
+
     def test_attribute_error(self):
         qs = Reader.objects.all().prefetch_related('books_read__xyz')
         with self.assertRaises(AttributeError) as cm:

This test fails with:

Traceback (most recent call last):
  File "/Users/myk/Documents/dev/django/tests/prefetch_related/tests.py", line 196, in test_reverse_one_to_one_then_m2m
    list(Author.objects.prefetch_related('bio__books').select_related('bio'))
  File "/Users/myk/Documents/dev/django/django/db/models/query.py", line 141, in __iter__
    self._fetch_all()
  File "/Users/myk/Documents/dev/django/django/db/models/query.py", line 965, in _fetch_all
    self._prefetch_related_objects()
  File "/Users/myk/Documents/dev/django/django/db/models/query.py", line 608, in _prefetch_related_objects
    prefetch_related_objects(self._result_cache, self._prefetch_related_lookups)
  File "/Users/myk/Documents/dev/django/django/db/models/query.py", line 1793, in prefetch_related_objects
    elif isinstance(getattr(first_obj, through_attr), list):
  File "/Users/myk/Documents/dev/django/django/db/models/fields/related.py", line 420, in __get__
    self.related.get_accessor_name()
RelatedObjectDoesNotExist: Author has no bio.

The regression exists in master and 1.7.x.

[loic84]

PR ​https://github.com/django/django/pull/2681.

[Tim Graham]

Actually tests don't pass on Python 3.

[Loic Bistuer <loic.bistuer@…>]

In bdf3473e64879d196e79fe8832cdacc6efb68150:

Fixed #22650 -- Fixed regression on prefetch_related.

Regression from f51c1f59 when using select_related then prefetch_related
on the reverse side of an O2O:

Author.objects.select_related('bio').prefetch_related('biobooks')

Thanks Aymeric Augustin for the report and tests. Refs #17001.

[Loic Bistuer <loic.bistuer@…>]

In 870b0a1f8689aa8fd4806623262228b8ac3a88a5:

Fixed the ordering of prefetch lookups so that latter lookups can refer to former lookups.

Thanks Anssi Kääriäinen and Tim Graham for the reviews. Refs #17001 and #22650.

[Loic Bistuer <loic.bistuer@…>]

In 24a41ecc3590f8d92d085d4a4caa5f8bf962ceae:

[1.7.x] Fixed #22650 -- Fixed regression on prefetch_related.

Regression from f51c1f59 when using select_related then prefetch_related
on the reverse side of an O2O:

Author.objects.select_related('bio').prefetch_related('biobooks')

Thanks Aymeric Augustin for the report and tests. Refs #17001.

Backport of bdf3473e64 from master

[Loic Bistuer <loic.bistuer@…>]

In 0fa1aeb8d8142bd6bceb0c9a36c8e42eeca21770:

[1.7.x] Fixed the ordering of prefetch lookups so that latter lookups can refer to former lookups.

Thanks Anssi Kääriäinen and Tim Graham for the reviews. Refs #17001 and #22650.

Backport of 870b0a1f86 from master