Use get_db_prep_value when getting instance attribute value in get_pr…

django/db/models/fields/related.py

@@ -1002,7 +1002,10 @@ def get_prefetch_queryset(self, instances, queryset=None):
                     getattr(result, '_prefetch_related_val_%s' % f.attname)
                     for f in fk.local_related_fields
                 ),
-                lambda inst: tuple(getattr(inst, f.attname) for f in fk.foreign_related_fields),
+                lambda inst: tuple(
+                    f.get_db_prep_value(getattr(inst, f.attname), connection)
+                    for f in fk.foreign_related_fields
+                ),
                 False,
                 self.prefetch_cache_name,
             )

docs/releases/1.8.3.txt

@@ -50,3 +50,6 @@ Bugfixes
 
 * Fixed recording of applied status for squashed (replacement) migrations
   (:ticket:`24628`).
+
+* Fixed prefetch_related for models using UUID primary keys on non-PostgreSQL
+  databases (:ticket:`24912`).

tests/prefetch_related/models.py

@@ -1,3 +1,4 @@
+import uuid
 from django.contrib.contenttypes.fields import (
     GenericForeignKey, GenericRelation,
 )
@@ -257,3 +258,11 @@ def __str__(self):
 
     class Meta:
         ordering = ['id']
+
+
+# Model for many-to-many with UUID pk test:
+
+class Pet(models.Model):
+    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
+    name = models.CharField(max_length=20)
+    people = models.ManyToManyField(Person, related_name='pets')

tests/prefetch_related/tests.py

@@ -12,7 +12,7 @@
 from .models import (
     Author, Author2, AuthorAddress, AuthorWithAge, Bio, Book, Bookmark,
     BookReview, BookWithYear, Comment, Department, Employee, FavoriteAuthors,
-    House, LessonEntry, Person, Qualification, Reader, Room, TaggedItem,
+    House, LessonEntry, Person, Pet, Qualification, Reader, Room, TaggedItem,
     Teacher, WordEntry,
 )
 
@@ -1161,3 +1161,20 @@ def test_bug(self):
         prefetcher = get_prefetcher(self.rooms[0], 'house')[0]
         queryset = prefetcher.get_prefetch_queryset(list(Room.objects.all()))[0]
         self.assertNotIn(' JOIN ', force_text(queryset.query))
+
+
+class UUIDPrefetchRelated(TestCase):
+    def setUp(self):
+        self.pet = Pet.objects.create(name='Fifi')
+        self.pet.people.add(
+            *[
+                Person.objects.create(name='Ellen'),
+                Person.objects.create(name='George'),
+            ]
+        )
+
+    def test_prefetch_related(self):
+        with self.assertNumQueries(2):
+            pet = Pet.objects.filter(pk=self.pet.pk).prefetch_related('people').first()
+        with self.assertNumQueries(0):
+            self.assertEqual(2, len(pet.people.all()))