Fixed #33322 -- Fixed loss of assigned related object when saving relation with bulk_update().

2 files changed, 5 insertions, 1 deletions

diff --git a/django/db/models/base.py b/django/db/models/base.py
index 29bbde5e6b..237a04cfd7 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -931,11 +931,13 @@ class Model(metaclass=ModelBase):
             using=using, raw=raw,
         )
 
-    def _prepare_related_fields_for_save(self, operation_name):
+    def _prepare_related_fields_for_save(self, operation_name, fields=None):
         # Ensure that a model instance without a PK hasn't been assigned to
         # a ForeignKey or OneToOneField on this model. If the field is
         # nullable, allowing the save would result in silent data loss.
         for field in self._meta.concrete_fields:
+            if fields and field not in fields:
+                continue
             # If the related field isn't cached, then an instance hasn't been
             # assigned and there's no need to worry about this check.
             if field.is_relation and field.is_cached(self):
diff --git a/django/db/models/query.py b/django/db/models/query.py
index fc36945f56..fb6639793a 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -549,6 +549,8 @@ class QuerySet:
             raise ValueError('bulk_update() cannot be used with primary key fields.')
         if not objs:
             return 0
+        for obj in objs:
+            obj._prepare_related_fields_for_save(operation_name='bulk_update', fields=fields)
         # PK is used twice in the resulting update query, once in the filter
         # and once in the WHEN. Each field will also have one CAST.
         connection = connections[self.db]