Fixed #27710 -- Made Model.save() invalidate cached, stale relations after a primary key assignment.

1 files changed, 4 insertions, 0 deletions

diff --git a/django/db/models/base.py b/django/db/models/base.py
index e8ef2db913..3f4d65571d 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -674,6 +674,10 @@ class Model(metaclass=ModelBase):
                         "save() prohibited to prevent data loss due to "
                         "unsaved related object '%s'." % field.name
                     )
+                # If the relationship's pk was changed, clear the cached
+                # relationship.
+                if obj and obj.pk != getattr(self, field.attname):
+                    field.delete_cached_value(self)
 
         using = using or router.db_for_write(self.__class__, instance=self)
         if force_insert and (force_update or update_fields):