Fixed #35073 -- Avoided unnecessary calling of callables used by SET/SET_DEFAULT in Collector.collect().

django/db/models/deletion.py

@@ -60,8 +60,9 @@ def SET(value):
         def set_on_delete(collector, field, sub_objs, using):
             collector.add_field_update(field, value, sub_objs)
 
+        set_on_delete.lazy_sub_objs = True
+
     set_on_delete.deconstruct = lambda: ("django.db.models.SET", (value,), {})
-    set_on_delete.lazy_sub_objs = True
     return set_on_delete
 
 
@@ -76,9 +77,6 @@ def SET_DEFAULT(collector, field, sub_objs, using):
     collector.add_field_update(field, field.get_default(), sub_objs)
 
 
-SET_DEFAULT.lazy_sub_objs = True
-
-
 def DO_NOTHING(collector, field, sub_objs, using):
     pass
 

tests/delete_regress/models.py

@@ -93,9 +93,6 @@ class Item(models.Model):
     location_value = models.ForeignKey(
         Location, models.SET(42), default=1, db_constraint=False, related_name="+"
     )
-    location_default = models.ForeignKey(
-        Location, models.SET_DEFAULT, default=1, db_constraint=False, related_name="+"
-    )
 
 
 # Models for #16128
@@ -151,3 +148,22 @@ class OrderedPerson(models.Model):
 
     class Meta:
         ordering = ["name"]
+
+
+def get_best_toy():
+    toy, _ = Toy.objects.get_or_create(name="best")
+    return toy
+
+
+def get_worst_toy():
+    toy, _ = Toy.objects.get_or_create(name="worst")
+    return toy
+
+
+class Collector(models.Model):
+    best_toy = models.ForeignKey(
+        Toy, default=get_best_toy, on_delete=models.SET_DEFAULT, related_name="toys"
+    )
+    worst_toy = models.ForeignKey(
+        Toy, models.SET(get_worst_toy), related_name="bad_toys"
+    )

tests/delete_regress/tests.py

@@ -408,9 +408,17 @@ class SetQueryCountTests(TestCase):
         Item.objects.create(
             version=version,
             location=location,
-            location_default=location,
             location_value=location,
         )
-        # 3 UPDATEs for SET of item values and one for DELETE locations.
-        with self.assertNumQueries(4):
+        # 2 UPDATEs for SET of item values and one for DELETE locations.
+        with self.assertNumQueries(3):
             location.delete()
+
+
+class SetCallableCollectorDefaultTests(TestCase):
+    def test_set(self):
+        # Collector doesn't call callables used by models.SET and
+        # models.SET_DEFAULT if not necessary.
+        Toy.objects.create(name="test")
+        Toy.objects.all().delete()
+        self.assertSequenceEqual(Toy.objects.all(), [])