Fixed #29078 -- Made serializers respect prefetch_related() for m2m fields.

2 files changed, 10 insertions, 4 deletions

diff --git a/django/core/serializers/python.py b/django/core/serializers/python.py
index 5a5d8a7036..0ceb676e90 100644
--- a/django/core/serializers/python.py
+++ b/django/core/serializers/python.py
@@ -67,9 +67,11 @@ class Serializer(base.Serializer):
             else:
                 def m2m_value(value):
                     return self._value_from_field(value, value._meta.pk)
-            self._current[field.name] = [
-                m2m_value(related) for related in getattr(obj, field.name).iterator()
-            ]
+            m2m_iter = getattr(obj, '_prefetched_objects_cache', {}).get(
+                field.name,
+                getattr(obj, field.name).iterator(),
+            )
+            self._current[field.name] = [m2m_value(related) for related in m2m_iter]
 
     def getvalue(self):
         return self.objects
diff --git a/django/core/serializers/xml_serializer.py b/django/core/serializers/xml_serializer.py
index 1f62c8e971..07de9428e7 100644
--- a/django/core/serializers/xml_serializer.py
+++ b/django/core/serializers/xml_serializer.py
@@ -132,7 +132,11 @@ class Serializer(base.Serializer):
                     self.xml.addQuickElement("object", attrs={
                         'pk': str(value.pk)
                     })
-            for relobj in getattr(obj, field.name).iterator():
+            m2m_iter = getattr(obj, '_prefetched_objects_cache', {}).get(
+                field.name,
+                getattr(obj, field.name).iterator(),
+            )
+            for relobj in m2m_iter:
                 handle_m2m(relobj)
 
             self.xml.endElement("field")