Fixed #28375 -- Fixed KeyError crash on reverse prefetch of a model with OneToOneField primary key to a non-pk field.

django/db/models/fields/related_descriptors.py

@@ -63,8 +63,6 @@ and two directions (forward and reverse) for a total of six combinations.
    ``ReverseManyToManyDescriptor``, use ``ManyToManyDescriptor`` instead.
 """
 
-from operator import attrgetter
-
 from django.db import connections, router, transaction
 from django.db.models import Q, signals
 from django.db.models.query import QuerySet
@@ -334,11 +332,8 @@ class ReverseOneToOneDescriptor:
             queryset = self.get_queryset()
         queryset._add_hints(instance=instances[0])
 
-        rel_obj_attr = attrgetter(self.related.field.attname)
-
-        def instance_attr(obj):
-            return obj.pk
-
+        rel_obj_attr = self.related.field.get_local_related_value
+        instance_attr = self.related.field.get_foreign_related_value
         instances_dict = {instance_attr(inst): inst for inst in instances}
         query = {'%s__in' % self.related.field.name: instances}
         queryset = queryset.filter(**query)

tests/prefetch_related/models.py

@@ -65,7 +65,12 @@ class BookWithYear(Book):
 
 
 class Bio(models.Model):
-    author = models.OneToOneField(Author, models.CASCADE)
+    author = models.OneToOneField(
+        Author,
+        models.CASCADE,
+        primary_key=True,
+        to_field='name',
+    )
     books = models.ManyToManyField(Book, blank=True)
 
 

tests/prefetch_related/tests.py

@@ -81,6 +81,23 @@ class PrefetchRelatedTests(TestCase):
             with self.assertRaises(BookWithYear.DoesNotExist):
                 book.bookwithyear
 
+    def test_onetoone_reverse_with_to_field_pk(self):
+        """
+        A model (Bio) with a OneToOneField primary key (author) that references
+        a non-pk field (name) on the related model (Author) is prefetchable.
+        """
+        Bio.objects.bulk_create([
+            Bio(author=self.author1),
+            Bio(author=self.author2),
+            Bio(author=self.author3),
+        ])
+        authors = Author.objects.filter(
+            name__in=[self.author1, self.author2, self.author3],
+        ).prefetch_related('bio')
+        with self.assertNumQueries(2):
+            for author in authors:
+                self.assertEqual(author.name, author.bio.author.name)
+
     def test_survives_clone(self):
         with self.assertNumQueries(2):
             [list(b.first_time_authors.all())