[1.8.x] Fixed #24912 -- Fixed prefetch_related failure for UUIDField primary keys

This resolves a problem on databases besides PostgreSQL when using
prefetch_related with a source model that uses a UUID primary key.

Backport of bfb5b7150f from master

django/db/models/fields/related.py

@@ -954,7 +954,10 @@ def create_many_related_manager(superclass, rel):
                     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

@@ -66,3 +66,6 @@ Bugfixes
 * Provided better backwards compatibility for the ``verbosity`` argument in
   ``optparse`` management commands by casting it to an integer
   (:ticket:`24769`).
+
+* Fixed ``prefetch_related()`` on databases other than PostgreSQL for models
+  using UUID primary keys (:ticket:`24912`).

tests/prefetch_related/models.py

@@ -1,3 +1,5 @@
+import uuid
+
 from django.contrib.contenttypes.fields import (
     GenericForeignKey, GenericRelation,
 )
@@ -257,3 +259,18 @@ class Author2(models.Model):
 
     class Meta:
         ordering = ['id']
+
+
+# Models 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')
+
+
+class Flea(models.Model):
+    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
+    current_room = models.ForeignKey(Room, related_name='fleas', null=True)
+    pets_visited = models.ManyToManyField(Pet, related_name='fleas_hosted')
+    people_visited = models.ManyToManyField(Person, related_name='fleas_hosted')

tests/prefetch_related/test_uuid.py

@@ -0,0 +1,95 @@
+from __future__ import unicode_literals
+
+from django.test import TestCase
+
+from .models import Flea, House, Person, Pet, Room
+
+
+class UUIDPrefetchRelated(TestCase):
+
+    def test_prefetch_related_from_uuid_model(self):
+        Pet.objects.create(name='Fifi').people.add(
+            Person.objects.create(name='Ellen'),
+            Person.objects.create(name='George'),
+        )
+
+        with self.assertNumQueries(2):
+            pet = Pet.objects.prefetch_related('people').get(name='Fifi')
+        with self.assertNumQueries(0):
+            self.assertEqual(2, len(pet.people.all()))
+
+    def test_prefetch_related_to_uuid_model(self):
+        Person.objects.create(name='Bella').pets.add(
+            Pet.objects.create(name='Socks'),
+            Pet.objects.create(name='Coffee'),
+        )
+
+        with self.assertNumQueries(2):
+            person = Person.objects.prefetch_related('pets').get(name='Bella')
+        with self.assertNumQueries(0):
+            self.assertEqual(2, len(person.pets.all()))
+
+    def test_prefetch_related_from_uuid_model_to_uuid_model(self):
+        fleas = [Flea.objects.create() for i in range(3)]
+        Pet.objects.create(name='Fifi').fleas_hosted.add(*fleas)
+        Pet.objects.create(name='Bobo').fleas_hosted.add(*fleas)
+
+        with self.assertNumQueries(2):
+            pet = Pet.objects.prefetch_related('fleas_hosted').get(name='Fifi')
+        with self.assertNumQueries(0):
+            self.assertEqual(3, len(pet.fleas_hosted.all()))
+
+        with self.assertNumQueries(2):
+            flea = Flea.objects.prefetch_related('pets_visited').get(pk=fleas[0].pk)
+        with self.assertNumQueries(0):
+            self.assertEqual(2, len(flea.pets_visited.all()))
+
+
+class UUIDPrefetchRelatedLookups(TestCase):
+
+    @classmethod
+    def setUpTestData(cls):
+        house = House.objects.create(name='Redwood', address='Arcata')
+        room = Room.objects.create(name='Racoon', house=house)
+        fleas = [Flea.objects.create(current_room=room) for i in range(3)]
+        pet = Pet.objects.create(name='Spooky')
+        pet.fleas_hosted.add(*fleas)
+        person = Person.objects.create(name='Bob')
+        person.houses.add(house)
+        person.pets.add(pet)
+        person.fleas_hosted.add(*fleas)
+
+    def test_from_uuid_pk_lookup_uuid_pk_integer_pk(self):
+        # From uuid-pk model, prefetch <uuid-pk model>.<integer-pk model>:
+        with self.assertNumQueries(4):
+            spooky = Pet.objects.prefetch_related('fleas_hosted__current_room__house').get(name='Spooky')
+        with self.assertNumQueries(0):
+            self.assertEqual('Racoon', spooky.fleas_hosted.all()[0].current_room.name)
+
+    def test_from_uuid_pk_lookup_integer_pk2_uuid_pk2(self):
+        # From uuid-pk model, prefetch <integer-pk model>.<integer-pk model>.<uuid-pk model>.<uuid-pk model>:
+        with self.assertNumQueries(5):
+            spooky = Pet.objects.prefetch_related('people__houses__rooms__fleas').get(name='Spooky')
+        with self.assertNumQueries(0):
+            self.assertEqual(3, len(spooky.people.all()[0].houses.all()[0].rooms.all()[0].fleas.all()))
+
+    def test_from_integer_pk_lookup_uuid_pk_integer_pk(self):
+        # From integer-pk model, prefetch <uuid-pk model>.<integer-pk model>:
+        with self.assertNumQueries(3):
+            racoon = Room.objects.prefetch_related('fleas__people_visited').get(name='Racoon')
+        with self.assertNumQueries(0):
+            self.assertEqual('Bob', racoon.fleas.all()[0].people_visited.all()[0].name)
+
+    def test_from_integer_pk_lookup_integer_pk_uuid_pk(self):
+        # From integer-pk model, prefetch <integer-pk model>.<uuid-pk model>:
+        with self.assertNumQueries(3):
+            redwood = House.objects.prefetch_related('rooms__fleas').get(name='Redwood')
+        with self.assertNumQueries(0):
+            self.assertEqual(3, len(redwood.rooms.all()[0].fleas.all()))
+
+    def test_from_integer_pk_lookup_integer_pk_uuid_pk_uuid_pk(self):
+        # From integer-pk model, prefetch <integer-pk model>.<uuid-pk model>.<uuid-pk model>:
+        with self.assertNumQueries(4):
+            redwood = House.objects.prefetch_related('rooms__fleas__pets_visited').get(name='Redwood')
+        with self.assertNumQueries(0):
+            self.assertEqual('Spooky', redwood.rooms.all()[0].fleas.all()[0].pets_visited.all()[0].name)