Ticket #29085: patch.diff

django/db/models/base.py

@@ -659 +659 @@
             # been assigned and there's no need to worry about this check.
             if field.is_relation and field.is_cached(self):
                 obj = getattr(self, field.name, None)
+                obj_pk = getattr(self, field.attname, None)
                 # A pk may have been assigned manually to a model instance not
                 # saved to the database (or auto-generated in a case like
                 # UUIDField), but we allow the save to proceed and rely on the
                 # database to raise an IntegrityError if applicable. If
                 # constraints aren't supported by the database, there's the
                 # unavoidable risk of data corruption.
-                if obj and obj.pk is None:
+                if obj and (obj.pk is None or obj_pk is None):
                     # Remove the object from a related instance cache.
                     if not field.remote_field.multiple:
                         field.remote_field.delete_cached_value(obj)
@@ -675 +676 @@
                     )
                 # If the relationship's pk was changed, clear the cached
                 # relationship.
-                if obj and obj.pk != getattr(self, field.attname):
+                if obj and obj.pk != obj_pk:
                     field.delete_cached_value(self)
 
         using = using or router.db_for_write(self.__class__, instance=self)

tests/many_to_one/tests.py

@@ -522 +522 @@
         self.assertIsNot(c.parent, p)
         self.assertEqual(c.parent, p)
 
+    def test_unsaved_object(self):
+        msg = "save() prohibited to prevent data loss due to unsaved related object 'parent'."
+        child = Child()
+        child.parent = Parent()
+        child.parent.save()
+        with self.assertRaisesMessage(ValueError, msg):
+            child.save()
+
     def test_fk_to_bigautofield(self):
         ch = City.objects.create(name='Chicago')
         District.objects.create(city=ch, name='Far South')