Refs #20203 -- Allowed adding custom default manager to the model state

If the only manager on the model is the default manager defined
by Django (`objects = models.Manager()`), this manager will not
be added to the model state. If it is custom, it needs to be
passed to the model state.

1 files changed, 4 insertions, 1 deletions

diff --git a/django/db/migrations/state.py b/django/db/migrations/state.py
index 33362ed06f..c865f139d7 100644
--- a/django/db/migrations/state.py
+++ b/django/db/migrations/state.py
@@ -465,7 +465,10 @@ class ModelState(object):
                 (name, instance) for name, (cc, instance) in
                 sorted(managers_mapping.items(), key=lambda v: v[1])
             ]
-            if managers == [(default_manager_name, models.Manager())]:
+            # If the only manager on the model is the default manager defined
+            # by Django (`objects = models.Manager()`), this manager will not
+            # be added to the model state.
+            if managers == [('objects', models.Manager())]:
                 managers = []
         else:
             managers = []