code: def to_internal_value(self, data):
          
          if not data:
              return None
          request = self._get_request()
          user = request.user
          try:
              obj = core_utils.instance_from_url(data, user=user)
              model = obj.__class__
          except ValueError:
              raise serializers.ValidationError(_('URL is invalid: %s.') % data)
          except (Resolver404, AttributeError, MultipleObjectsReturned, ObjectDoesNotExist):
              raise serializers.ValidationError(_("Can't restore object from url: %s") % data)
          if model not in self.related_models:
              raise serializers.ValidationError(_('%s object does not support such relationship.') % six.text_type(obj))
          return obj
docs: Restores model instance from its url