code: def to_representation(self, instance):
          
          if self.id_only():
              return instance.pk
  
          pk = getattr(instance, 'pk', None)
          if not settings.ENABLE_SERIALIZER_OBJECT_CACHE or pk is None:
              return self._to_representation(instance)
          else:
              if pk not in self.obj_cache:
                  self.obj_cache[pk] = self._to_representation(instance)
              return self.obj_cache[pk]
docs: Modified to_representation method. Optionally may cache objects.
  
          Arguments:
              instance: A model instance or data object.
          Returns:
              Instance ID if the serializer is meant to represent its ID.
              Otherwise, a tagged data dict representation.