Fixed #18309 - Prefetch related does not work for fkey to multitable inherited model

Thanks to milosu for the report, tests and initial patch.

django/db/models/fields/related.py

@@ -329,10 +329,10 @@ class ReverseSingleRelatedObjectDescriptor(object):
             return QuerySet(self.field.rel.to).using(db)
 
     def get_prefetch_query_set(self, instances):
-        rel_obj_attr = attrgetter(self.field.rel.field_name)
+        other_field = self.field.rel.get_related_field()
+        rel_obj_attr = attrgetter(other_field.attname)
         instance_attr = attrgetter(self.field.attname)
         instances_dict = dict((instance_attr(inst), inst) for inst in instances)
-        other_field = self.field.rel.get_related_field()
         if other_field.rel:
             params = {'%s__pk__in' % self.field.rel.field_name: instances_dict.keys()}
         else:

tests/modeltests/prefetch_related/models.py

@@ -68,6 +68,9 @@ class Reader(models.Model):
     class Meta:
         ordering = ['id']
 
+class BookReview(models.Model):
+    book = models.ForeignKey(BookWithYear)
+    notes = models.TextField(null=True, blank=True)
 
 ## Models for default manager tests
 

tests/modeltests/prefetch_related/tests.py

@@ -7,7 +7,7 @@ from django.test.utils import override_settings
 
 from .models import (Author, Book, Reader, Qualification, Teacher, Department,
     TaggedItem, Bookmark, AuthorAddress, FavoriteAuthors, AuthorWithAge,
-    BookWithYear, Person, House, Room, Employee, Comment)
+    BookWithYear, BookReview, Person, House, Room, Employee, Comment)
 
 
 class PrefetchRelatedTests(TestCase):
@@ -335,6 +335,10 @@ class MultiTableInheritanceTest(TestCase):
         self.authorAddress = AuthorAddress.objects.create(
             author=self.author1, address='SomeStreet 1')
         self.book2.aged_authors.add(self.author2, self.author3)
+        self.br1 = BookReview.objects.create(
+            book=self.book1, notes="review book1")
+        self.br2 = BookReview.objects.create(
+            book=self.book2, notes="review book2")
 
     def test_foreignkey(self):
         with self.assertNumQueries(2):
@@ -343,6 +347,12 @@ class MultiTableInheritanceTest(TestCase):
                          for obj in qs]
         self.assertEqual(addresses, [[unicode(self.authorAddress)], [], []])
 
+    def test_foreignkey_to_inherited(self):
+        with self.assertNumQueries(2):
+            qs = BookReview.objects.prefetch_related('book')
+            titles = [obj.book.title for obj in qs]
+        self.assertEquals(titles, ["Poems", "More poems"])
+
     def test_m2m_to_inheriting_model(self):
         qs = AuthorWithAge.objects.prefetch_related('books_with_year')
         with self.assertNumQueries(2):