Fixed #24067 -- Renamed content types upon model renaming.

Thanks to Tim for the extensive review.

2 files changed, 88 insertions, 3 deletions

diff --git a/django/contrib/contenttypes/apps.py b/django/contrib/contenttypes/apps.py
index f6c3d430fd..e5708adc99 100644
--- a/django/contrib/contenttypes/apps.py
+++ b/django/contrib/contenttypes/apps.py
@@ -1,10 +1,12 @@
 from django.apps import AppConfig
 from django.contrib.contenttypes.checks import check_generic_foreign_keys
 from django.core import checks
-from django.db.models.signals import post_migrate
+from django.db.models.signals import post_migrate, pre_migrate
 from django.utils.translation import ugettext_lazy as _
 
-from .management import update_contenttypes
+from .management import (
+    inject_rename_contenttypes_operations, update_contenttypes,
+)
 
 
 class ContentTypesConfig(AppConfig):
@@ -12,5 +14,6 @@ class ContentTypesConfig(AppConfig):
     verbose_name = _("Content Types")
 
     def ready(self):
+        pre_migrate.connect(inject_rename_contenttypes_operations, sender=self)
         post_migrate.connect(update_contenttypes)
         checks.register(check_generic_foreign_keys, checks.Tags.models)
diff --git a/django/contrib/contenttypes/management.py b/django/contrib/contenttypes/management.py
index 7af1a78e36..0bdf8ed9fa 100644
--- a/django/contrib/contenttypes/management.py
+++ b/django/contrib/contenttypes/management.py
@@ -1,9 +1,91 @@
 from django.apps import apps as global_apps
-from django.db import DEFAULT_DB_ALIAS, router
+from django.db import DEFAULT_DB_ALIAS, migrations, router, transaction
+from django.db.utils import IntegrityError
 from django.utils import six
 from django.utils.six.moves import input
 
 
+class RenameContentType(migrations.RunPython):
+    def __init__(self, app_label, old_model, new_model):
+        self.app_label = app_label
+        self.old_model = old_model
+        self.new_model = new_model
+        super(RenameContentType, self).__init__(self.rename_forward, self.rename_backward)
+
+    def _rename(self, apps, schema_editor, old_model, new_model):
+        ContentType = apps.get_model('contenttypes', 'ContentType')
+        db = schema_editor.connection.alias
+        if not router.allow_migrate_model(db, ContentType):
+            return
+
+        try:
+            content_type = ContentType.objects.db_manager(db).get_by_natural_key(self.app_label, old_model)
+        except ContentType.DoesNotExist:
+            pass
+        else:
+            content_type.model = new_model
+            try:
+                with transaction.atomic(using=db):
+                    content_type.save(update_fields={'model'})
+            except IntegrityError:
+                # Gracefully fallback if a stale content type causes a
+                # conflict as update_contenttypes will take care of asking the
+                # user what should be done next.
+                content_type.model = old_model
+            else:
+                # Clear the cache as the `get_by_natual_key()` call will cache
+                # the renamed ContentType instance by its old model name.
+                ContentType.objects.clear_cache()
+
+    def rename_forward(self, apps, schema_editor):
+        self._rename(apps, schema_editor, self.old_model, self.new_model)
+
+    def rename_backward(self, apps, schema_editor):
+        self._rename(apps, schema_editor, self.new_model, self.old_model)
+
+
+def inject_rename_contenttypes_operations(plan=None, apps=global_apps, using=DEFAULT_DB_ALIAS, **kwargs):
+    """
+    Insert a `RenameContentType` operation after every planned `RenameModel`
+    operation.
+    """
+    if plan is None:
+        return
+
+    # Determine whether or not the ContentType model is available.
+    try:
+        ContentType = apps.get_model('contenttypes', 'ContentType')
+    except LookupError:
+        available = False
+    else:
+        if not router.allow_migrate_model(using, ContentType):
+            return
+        available = True
+
+    for migration, backward in plan:
+        if ((migration.app_label, migration.name) == ('contenttypes', '0001_initial')):
+            # There's no point in going forward if the initial contenttypes
+            # migration is unapplied as the ContentType model will be
+            # unavailable from this point.
+            if backward:
+                break
+            else:
+                available = True
+                continue
+        # The ContentType model is not available yet.
+        if not available:
+            continue
+        inserts = []
+        for index, operation in enumerate(migration.operations):
+            if isinstance(operation, migrations.RenameModel):
+                operation = RenameContentType(
+                    migration.app_label, operation.old_name_lower, operation.new_name_lower
+                )
+                inserts.append((index + 1, operation))
+        for inserted, (index, operation) in enumerate(inserts):
+            migration.operations.insert(inserted + index, operation)
+
+
 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