[2.2.x] Fixed #30330 -- Fixed setting of primary key to None during fast-delete.

Regression in bc7dd8490b.

Backport of afc708cf6d from master

django/db/models/deletion.py

@@ -278,6 +278,7 @@ class Collector:
             if self.can_fast_delete(instance):
                 with transaction.mark_for_rollback_on_error():
                     count = sql.DeleteQuery(model).delete_batch([instance.pk], self.using)
+                setattr(instance, model._meta.pk.attname, None)
                 return count, {model._meta.label: count}
 
         with transaction.atomic(using=self.using, savepoint=False):

docs/releases/2.2.1.txt

@@ -22,3 +22,6 @@ Bugfixes
   :class:`~django.contrib.postgres.aggregates.ArrayAgg` and
   :class:`~django.contrib.postgres.aggregates.StringAgg` when it contains an
   expression with params (:ticket:`30332`).
+
+* Fixed a regression in Django 2.2 that caused a single instance fast-delete
+  to not set the primary key to ``None`` (:ticket:`30330`).

tests/delete/tests.py

@@ -1,6 +1,7 @@
 from math import ceil
 
 from django.db import IntegrityError, connection, models
+from django.db.models.deletion import Collector
 from django.db.models.sql.constants import GET_ITERATOR_CHUNK_SIZE
 from django.test import TestCase, skipIfDBFeature, skipUnlessDBFeature
 
@@ -471,6 +472,14 @@ class FastDeleteTests(TestCase):
         self.assertEqual(User.objects.count(), 1)
         self.assertTrue(User.objects.filter(pk=u2.pk).exists())
 
+    def test_fast_delete_instance_set_pk_none(self):
+        u = User.objects.create()
+        # User can be fast-deleted.
+        collector = Collector(using='default')
+        self.assertTrue(collector.can_fast_delete(u))
+        u.delete()
+        self.assertIsNone(u.pk)
+
     def test_fast_delete_joined_qs(self):
         a = Avatar.objects.create(desc='a')
         User.objects.create(avatar=a)