Fixed #33937 -- Optimized serialization of related m2m fields without natural keys.

1 files changed, 7 insertions, 1 deletions

diff --git a/django/core/serializers/python.py b/django/core/serializers/python.py
index a3918bf9d2..fa3bce2948 100644
--- a/django/core/serializers/python.py
+++ b/django/core/serializers/python.py
@@ -70,14 +70,20 @@ class Serializer(base.Serializer):
                 def m2m_value(value):
                     return value.natural_key()
 
+                def queryset_iterator(obj, field):
+                    return getattr(obj, field.name).iterator()
+
             else:
 
                 def m2m_value(value):
                     return self._value_from_field(value, value._meta.pk)
 
+                def queryset_iterator(obj, field):
+                    return getattr(obj, field.name).only("pk").iterator()
+
             m2m_iter = getattr(obj, "_prefetched_objects_cache", {}).get(
                 field.name,
-                getattr(obj, field.name).iterator(),
+                queryset_iterator(obj, field),
             )
             self._current[field.name] = [m2m_value(related) for related in m2m_iter]