Fixed #18682 -- Expanded explanation in stale content type deletion. (#6869)

django/contrib/contenttypes/management.py

 from django.apps import apps as global_apps
 from django.db import DEFAULT_DB_ALIAS, migrations, router, transaction
+from django.db.models.deletion import Collector
 from django.db.utils import IntegrityError
 from django.utils import six
 from django.utils.six.moves import input
@@ -141,21 +142,39 @@ def update_contenttypes(app_config, verbosity=2, interactive=True, using=DEFAULT
             print("Adding content type '%s | %s'" % (ct.app_label, ct.model))
 
     # Confirm that the content type is stale before deletion.
+    using = router.db_for_write(ContentType)
     if to_remove:
         if interactive:
-            content_type_display = '\n'.join(
-                '    %s | %s' % (ct.app_label, ct.model)
-                for ct in to_remove
-            )
-            ok_to_delete = input("""The following content types are stale and need to be deleted:
+            ct_info = []
+            for ct in to_remove:
+                ct_info.append('    - Content type for %s.%s' % (ct.app_label, ct.model))
+                collector = NoFastDeleteCollector(using=using)
+                collector.collect([ct])
+
+                for obj_type, objs in collector.data.items():
+                    if objs == {ct}:
+                        continue
+                    ct_info.append('    - %s object%s of type %s.%s:' % (
+                        len(objs),
+                        's' if len(objs) != 1 else '',
+                        obj_type._meta.app_label,
+                        obj_type._meta.model_name)
+                    )
+
+            content_type_display = '\n'.join(ct_info)
+            print("""Some content types in your database are stale and can be deleted.
+Any objects that depend on these content types will then also be deleted.
+The content types, and the dependent objects that would be deleted, are:
 
 %s
 
-Any objects related to these content types by a foreign key will also
-be deleted. Are you sure you want to delete these content types?
-If you're unsure, answer 'no'.
+This list does not include data that might be in your database
+outside of Django's models.
 
-    Type 'yes' to continue, or 'no' to cancel: """ % content_type_display)
+Are you sure you want to delete these content types?
+If you're unsure, answer 'no'.
+    """ % content_type_display)
+            ok_to_delete = input("Type 'yes' to continue, or 'no' to cancel: ")
         else:
             ok_to_delete = False
 
@@ -167,3 +186,12 @@ If you're unsure, answer 'no'.
         else:
             if verbosity >= 2:
                 print("Stale content types remain.")
+
+
+class NoFastDeleteCollector(Collector):
+    def can_fast_delete(self, *args, **kwargs):
+        """
+        We always want to load the objects into memory so that we can display
+        them to the user when asking confirmation.
+        """
+        return False

docs/releases/1.11.txt

@@ -73,7 +73,10 @@ Minor features
 :mod:`django.contrib.contenttypes`
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-* ...
+* When stale content types are detected during a management command, there is
+  now an expansive list of objects that will be deleted. Previously, only
+  the content type objects themselves were listed, even if there were objects
+  with foreign keys towards the content types that would be deleted also.
 
 :mod:`django.contrib.gis`
 ~~~~~~~~~~~~~~~~~~~~~~~~~

tests/contenttypes_tests/tests.py

@@ -20,7 +20,7 @@ from django.test.utils import captured_stdout, isolate_apps
 from django.utils.encoding import force_str, force_text
 
 from .models import (
-    Article, Author, ModelWithNullFKToSite, SchemeIncludedURL,
+    Article, Author, ModelWithNullFKToSite, Post, SchemeIncludedURL,
     Site as MockSite,
 )
 
@@ -383,13 +383,27 @@ class GenericRelationshipTests(SimpleTestCase):
 class UpdateContentTypesTests(TestCase):
     def setUp(self):
         self.before_count = ContentType.objects.count()
-        ContentType.objects.create(app_label='contenttypes_tests', model='Fake')
+        self.content_type = ContentType.objects.create(app_label='contenttypes_tests', model='Fake')
         self.app_config = apps.get_app_config('contenttypes_tests')
 
-    def test_interactive_true(self):
+    def test_interactive_true_with_dependent_objects(self):
         """
         interactive mode of update_contenttypes() (the default) should delete
-        stale contenttypes.
+        stale contenttypes and warn of dependent objects
+        """
+        Post.objects.create(title='post', content_type=self.content_type)
+        contenttypes_management.input = lambda x: force_str("yes")
+        with captured_stdout() as stdout:
+            contenttypes_management.update_contenttypes(self.app_config)
+        self.assertEqual(Post.objects.count(), 0)
+        self.assertIn("1 object of type contenttypes_tests.post:", stdout.getvalue())
+        self.assertIn("Deleting stale content type", stdout.getvalue())
+        self.assertEqual(ContentType.objects.count(), self.before_count)
+
+    def test_interactive_true_without_dependent_objects(self):
+        """
+        interactive mode of update_contenttypes() (the default) should delete
+        stale contenttypes and inform there are no dependent objects
         """
         contenttypes_management.input = lambda x: force_str("yes")
         with captured_stdout() as stdout: