def get_db_prep_save(self, value, **kwargs):
    return super(JSONField, self).get_db_prep_save(value, **kwargs)


class CompressedJSONField(JSONField, CompressedField, metaclass=models.SubfieldBase):
    pass


class TestModel(models.Model):
    name = models.CharField(max_length=150)
compressed_json_field = CompressedJSONField()

def __unicode__(self):
    return self.name
Пользовательское поле Django с множественным наследованием