Check for ContentType and Permission models before migration (#11184)

This prevents `create_extra_permissions` from querying or creating
ContentType or Permission objects if the models cannot be found.
When using multiple databases which do not have the auth_permission
table `create_extra_permissions` will cause migrate to fail.

This is similar to https://code.djangoproject.com/ticket/24075.

Thanks to @crccheck for additional bug reporting.

CHANGELOG.txt

@@ -51,6 +51,7 @@ Changelog
  * Fix: Fix crash when using the locale switcher on the snippets create view (Sage Abdullah)
  * Fix: Fix performance regression on reports from calling `decorate_paginated_queryset` before pagination / filtering (Alex Tomkins)
  * Fix: Make searching on specific fields work correctly on Elasticsearch when boost is in use (Matt Westcott)
+ * Fix: Prevent snippet permission post-migrate hook from failing on multiple database configurations (Joe Tsoi)
  * Docs: Fix code example for `{% picture ... as ... %}` template tag (Rezyapkin)
 
 

CONTRIBUTORS.md

@@ -767,6 +767,7 @@
 * Andrey Nehaychik
 * Meli Imelda
 * Kehinde Bobade
+* Joe Tsoi
 
 ## Translators
 

docs/releases/5.2.1.md

@@ -24,6 +24,7 @@ depth: 1
  * Fix crash when using the locale switcher on the snippets create view (Sage Abdullah)
  * Fix performance regression on reports from calling `decorate_paginated_queryset` before pagination / filtering (Alex Tomkins)
  * Make searching on specific fields work correctly on Elasticsearch when boost is in use (Matt Westcott)
+ * Prevent snippet permission post-migrate hook from failing on multiple database configurations (Joe Tsoi)
 
 ### Documentation
 

wagtail/snippets/models.py

@@ -1,10 +1,11 @@
 from functools import lru_cache
 
+from django.apps import apps as global_apps
 from django.contrib.admin.utils import quote
 from django.contrib.auth import get_permission_codename
 from django.contrib.auth.models import Permission
 from django.contrib.contenttypes.models import ContentType
-from django.db import DEFAULT_DB_ALIAS, models
+from django.db import DEFAULT_DB_ALIAS, models, router
 from django.urls import reverse
 from django.utils.module_loading import import_string
 
@@ -120,8 +121,21 @@ def register_deferred_snippets():
         _register_snippet_immediately(registerable, viewset)
 
 
-def create_extra_permissions(*args, using=DEFAULT_DB_ALIAS, **kwargs):
-    model_cts = ContentType.objects.get_for_models(
+def create_extra_permissions(
+    app_config, *args, using=DEFAULT_DB_ALIAS, apps=global_apps, **kwargs
+):
+    app_label = app_config.label
+    try:
+        app_config = apps.get_app_config(app_label)
+        apps.get_model("contenttypes", "ContentType")
+        apps.get_model("auth", "Permission")
+    except LookupError:
+        return
+
+    if not router.allow_migrate_model(using, Permission):
+        return
+
+    model_cts = ContentType.objects.db_manager(using).get_for_models(
         *get_snippet_models(), for_concrete_models=False
     )
 

wagtail/snippets/tests/test_management.py

@@ -0,0 +1,26 @@
+from django.apps import apps
+from django.contrib.contenttypes.models import ContentType
+from django.db import migrations
+from django.test import TestCase
+
+from wagtail.snippets.models import create_extra_permissions
+
+
+class TestCreatePermissions(TestCase):
+    def setUp(self):
+        self.app_config = apps.get_app_config("auth")
+
+    def tearDown(self):
+        ContentType.objects.clear_cache()
+
+    def test_unavailable_models(self):
+        state = migrations.state.ProjectState()
+
+        # Unavailable contenttypes.ContentType
+        with self.assertNumQueries(0):
+            create_extra_permissions(self.app_config, verbosity=0, apps=state.apps)
+
+        # Unavailable auth.Permission
+        state = migrations.state.ProjectState(real_apps={"contenttypes"})
+        with self.assertNumQueries(0):
+            create_extra_permissions(self.app_config, verbosity=0, apps=state.apps)