[4.2.x] Fixed #34620 -- Fixed serialization crash on m2m fields without natural keys when base querysets use select_related().

Regression in 19e0587ee596debf77540d6a08ccb6507e60b6a7.

Thanks Martin Svoboda for the report.
Backport of f9936deed1ff13b20e18bd9ca2b0750b52706b6c from main

2 files changed, 6 insertions, 2 deletions

diff --git a/django/core/serializers/python.py b/django/core/serializers/python.py
index 36048601af..0dc504aa34 100644
--- a/django/core/serializers/python.py
+++ b/django/core/serializers/python.py
@@ -79,7 +79,9 @@ class Serializer(base.Serializer):
                     return self._value_from_field(value, value._meta.pk)
 
                 def queryset_iterator(obj, field):
-                    return getattr(obj, field.name).only("pk").iterator()
+                    return (
+                        getattr(obj, field.name).select_related().only("pk").iterator()
+                    )
 
             m2m_iter = getattr(obj, "_prefetched_objects_cache", {}).get(
                 field.name,
diff --git a/django/core/serializers/xml_serializer.py b/django/core/serializers/xml_serializer.py
index 1d3269c41a..e0129a59bb 100644
--- a/django/core/serializers/xml_serializer.py
+++ b/django/core/serializers/xml_serializer.py
@@ -155,7 +155,9 @@ class Serializer(base.Serializer):
                     self.xml.addQuickElement("object", attrs={"pk": str(value.pk)})
 
                 def queryset_iterator(obj, field):
-                    return getattr(obj, field.name).only("pk").iterator()
+                    return (
+                        getattr(obj, field.name).select_related().only("pk").iterator()
+                    )
 
             m2m_iter = getattr(obj, "_prefetched_objects_cache", {}).get(
                 field.name,