Fixed #18676 -- Allow fast-path deletion of objects

Objects can be fast-path deleted if there are no signals, and there are
no further cascades. If fast-path is taken, the objects do not need to
be loaded into memory before deletion.

Thanks to Jeremy Dunck, Simon Charette and Alex Gaynor for reviewing
the patch.

2 files changed, 15 insertions, 1 deletions

diff --git a/tests/regressiontests/admin_util/models.py b/tests/regressiontests/admin_util/models.py
index b3504a1fa4..32a6cd6291 100644
--- a/tests/regressiontests/admin_util/models.py
+++ b/tests/regressiontests/admin_util/models.py
@@ -39,3 +39,6 @@ class Guest(models.Model):
 
     class Meta:
         verbose_name = "awesome guest"
+
+class EventGuide(models.Model):
+    event = models.ForeignKey(Event, on_delete=models.DO_NOTHING)
diff --git a/tests/regressiontests/admin_util/tests.py b/tests/regressiontests/admin_util/tests.py
index d04740ce95..ef8a91d1db 100644
--- a/tests/regressiontests/admin_util/tests.py
+++ b/tests/regressiontests/admin_util/tests.py
@@ -17,7 +17,7 @@ from django.utils.formats import localize
 from django.utils.safestring import mark_safe
 from django.utils import six
 
-from .models import Article, Count, Event, Location
+from .models import Article, Count, Event, Location, EventGuide
 
 
 class NestedObjectsTests(TestCase):
@@ -71,6 +71,17 @@ class NestedObjectsTests(TestCase):
         # Should not require additional queries to populate the nested graph.
         self.assertNumQueries(2, self._collect, 0)
 
+    def test_on_delete_do_nothing(self):
+        """
+        Check that the nested collector doesn't query for DO_NOTHING objects.
+        """
+        n = NestedObjects(using=DEFAULT_DB_ALIAS)
+        objs = [Event.objects.create()]
+        EventGuide.objects.create(event=objs[0])
+        with self.assertNumQueries(2):
+            # One for Location, one for Guest, and no query for EventGuide
+            n.collect(objs)
+
 class UtilTests(unittest.TestCase):
     def test_values_from_lookup_field(self):
         """