Fixed #24075 -- Used post-migration models in contrib apps receivers.

Thanks Markus and Tim for the review.

django/contrib/auth/management/__init__.py

@@ -6,7 +6,7 @@ from __future__ import unicode_literals
 import getpass
 import unicodedata
 
-from django.apps import apps
+from django.apps import apps as global_apps
 from django.contrib.auth import get_permission_codename
 from django.core import exceptions
 from django.db import DEFAULT_DB_ALIAS, router
@@ -37,11 +37,14 @@ def _get_builtin_permissions(opts):
     return perms
 
 
-def create_permissions(app_config, verbosity=2, interactive=True, using=DEFAULT_DB_ALIAS, **kwargs):
+def create_permissions(app_config, verbosity=2, interactive=True, using=DEFAULT_DB_ALIAS, apps=global_apps, **kwargs):
     if not app_config.models_module:
         return
 
+    app_label = app_config.label
     try:
+        app_config = apps.get_app_config(app_label)
+        ContentType = apps.get_model('contenttypes', 'ContentType')
         Permission = apps.get_model('auth', 'Permission')
     except LookupError:
         return
@@ -49,8 +52,6 @@ def create_permissions(app_config, verbosity=2, interactive=True, using=DEFAULT_
     if not router.allow_migrate_model(using, Permission):
         return
 
-    from django.contrib.contenttypes.models import ContentType
-
     # This will hold the permissions we're looking for as
     # (content_type, (codename, name))
     searched_perms = list()

django/contrib/contenttypes/management.py

@@ -1,10 +1,10 @@
-from django.apps import apps
+from django.apps import apps as global_apps
 from django.db import DEFAULT_DB_ALIAS, router
 from django.utils import six
 from django.utils.six.moves import input
 
 
-def update_contenttypes(app_config, verbosity=2, interactive=True, using=DEFAULT_DB_ALIAS, **kwargs):
+def update_contenttypes(app_config, verbosity=2, interactive=True, using=DEFAULT_DB_ALIAS, apps=global_apps, **kwargs):
     """
     Creates content types for models in the given app, removing any model
     entries that no longer have a matching model class.
@@ -12,7 +12,9 @@ def update_contenttypes(app_config, verbosity=2, interactive=True, using=DEFAULT
     if not app_config.models_module:
         return
 
+    app_label = app_config.label
     try:
+        app_config = apps.get_app_config(app_label)
         ContentType = apps.get_model('contenttypes', 'ContentType')
     except LookupError:
         return
@@ -21,8 +23,9 @@ def update_contenttypes(app_config, verbosity=2, interactive=True, using=DEFAULT
         return
 
     ContentType.objects.clear_cache()
-
-    app_label = app_config.label
+    # Always clear the global content types cache.
+    if apps is not global_apps:
+        global_apps.get_model('contenttypes', 'ContentType').objects.clear_cache()
 
     app_models = {
         model._meta.model_name: model

django/contrib/contenttypes/models.py

@@ -2,7 +2,6 @@ from __future__ import unicode_literals
 
 from django.apps import apps
 from django.db import models
-from django.db.utils import IntegrityError, OperationalError, ProgrammingError
 from django.utils.encoding import force_text, python_2_unicode_compatible
 from django.utils.translation import ugettext_lazy as _
 
@@ -48,24 +47,15 @@ class ContentTypeManager(models.Manager):
         # The ContentType entry was not found in the cache, therefore we
         # proceed to load or create it.
         try:
-            try:
-                # We start with get() and not get_or_create() in order to use
-                # the db_for_read (see #20401).
-                ct = self.get(app_label=opts.app_label, model=opts.model_name)
-            except self.model.DoesNotExist:
-                # Not found in the database; we proceed to create it.  This time we
-                # use get_or_create to take care of any race conditions.
-                ct, created = self.get_or_create(
-                    app_label=opts.app_label,
-                    model=opts.model_name,
-                )
-        except (OperationalError, ProgrammingError, IntegrityError):
-            # It's possible to migrate a single app before contenttypes,
-            # as it's not a required initial dependency (it's contrib!)
-            # Have a nice error for this.
-            raise RuntimeError(
-                "Error creating new content types. Please make sure contenttypes "
-                "is migrated before trying to migrate apps individually."
+            # Start with get() and not get_or_create() in order to use
+            # the db_for_read (see #20401).
+            ct = self.get(app_label=opts.app_label, model=opts.model_name)
+        except self.model.DoesNotExist:
+            # Not found in the database; we proceed to create it. This time
+            # use get_or_create to take care of any race conditions.
+            ct, created = self.get_or_create(
+                app_label=opts.app_label,
+                model=opts.model_name,
             )
         self._add_to_cache(self.db, ct)
         return ct

django/contrib/sites/management.py

@@ -2,13 +2,13 @@
 Creates the default Site object.
 """
 
-from django.apps import apps
+from django.apps import apps as global_apps
 from django.conf import settings
 from django.core.management.color import no_style
 from django.db import DEFAULT_DB_ALIAS, connections, router
 
 
-def create_default_site(app_config, verbosity=2, interactive=True, using=DEFAULT_DB_ALIAS, **kwargs):
+def create_default_site(app_config, verbosity=2, interactive=True, using=DEFAULT_DB_ALIAS, apps=global_apps, **kwargs):
     try:
         Site = apps.get_model('sites', 'Site')
     except LookupError: