Fixed #26643 -- Prevented unnecessary AlterModelManagers operations caused by the manager inheritance refactor.

This also makes migrations respect the base_manager_name and
default_manager_name model options.

Thanks Anthony King and Matthew Schinckel for the initial patches.

2 files changed, 31 insertions, 26 deletions

diff --git a/django/db/migrations/operations/models.py b/django/db/migrations/operations/models.py
index 1a3b523820..b7d4046f87 100644
--- a/django/db/migrations/operations/models.py
+++ b/django/db/migrations/operations/models.py
@@ -665,6 +665,8 @@ class AlterModelOptions(ModelOptionOperation):
 
     # Model options we want to compare and preserve in an AlterModelOptions op
     ALTER_OPTION_KEYS = [
+        "base_manager_name",
+        "default_manager_name",
         "get_latest_by",
         "managed",
         "ordering",
diff --git a/django/db/migrations/state.py b/django/db/migrations/state.py
index 9bb618e03e..44eab227ed 100644
--- a/django/db/migrations/state.py
+++ b/django/db/migrations/state.py
@@ -1,6 +1,7 @@
 from __future__ import unicode_literals
 
 import copy
+import warnings
 from collections import OrderedDict
 from contextlib import contextmanager
 
@@ -13,6 +14,7 @@ from django.db.models.fields.related import RECURSIVE_RELATIONSHIP_CONSTANT
 from django.db.models.options import DEFAULT_NAMES, normalize_together
 from django.db.models.utils import make_model_tuple
 from django.utils import six
+from django.utils.deprecation import RemovedInDjango20Warning
 from django.utils.encoding import force_text, smart_text
 from django.utils.functional import cached_property
 from django.utils.module_loading import import_string
@@ -444,28 +446,24 @@ class ModelState(object):
             bases = (models.Model,)
 
         managers = []
-
-        # Make sure the default manager is always first since ordering chooses
-        # the default manager.
-        if not model._default_manager.auto_created:
-            if model._default_manager.use_in_migrations:
-                default_manager = copy.copy(model._default_manager)
-                default_manager._set_creation_counter()
-
-            # If the default manager doesn't have `use_in_migrations = True`,
-            # shim a default manager so another manager isn't promoted in its
-            # place.
+        default_manager_shim = None
+        for manager in model._meta.managers:
+            if manager.use_in_migrations:
+                new_manager = copy.copy(manager)
+                new_manager._set_creation_counter()
+            elif manager is model._base_manager or manager is model._default_manager:
+                new_manager = models.Manager()
+                new_manager.model = manager.model
+                new_manager.name = manager.name
+                if manager is model._default_manager:
+                    default_manager_shim = new_manager
             else:
-                default_manager = models.Manager()
-                default_manager.model = model
-                default_manager.name = model._default_manager.name
-            managers.append((force_text(default_manager.name), default_manager))
+                continue
+            managers.append((force_text(manager.name), new_manager))
 
-        for manager in model._meta.managers:
-            if manager.use_in_migrations and manager is not model._default_manager:
-                manager = copy.copy(manager)
-                manager._set_creation_counter()
-                managers.append((force_text(manager.name), manager))
+        # Ignore a shimmed default manager called objects if it's the only one.
+        if managers == [('objects', default_manager_shim)]:
+            managers = []
 
         # Construct the new ModelState
         return cls(
@@ -541,12 +539,17 @@ class ModelState(object):
         # Restore managers
         body.update(self.construct_managers())
 
-        # Then, make a Model object (apps.register_model is called in __new__)
-        return type(
-            str(self.name),
-            bases,
-            body,
-        )
+        with warnings.catch_warnings():
+            warnings.filterwarnings(
+                "ignore", "Managers from concrete parents will soon qualify as default managers",
+                RemovedInDjango20Warning)
+
+            # Then, make a Model object (apps.register_model is called in __new__)
+            return type(
+                str(self.name),
+                bases,
+                body,
+            )
 
     def get_field_by_name(self, name):
         for fname, field in self.fields: