Python 2.7 在Google App Engine python ndb中的同一实体内创建实体的实例

如何在同一实体中创建实体的实例。我想要的是：

class User(ndb.model):
    friends = ndb.StructuredProperty( User, repeated=True )

---

您可以在创建模型后动态更新模型：

class User(ndb.Model):
  pass

User.friends = ndb.StructuredProperty(User, repeated=True)
User._fix_up_properties()

\u修复属性

来源描述：

def _fix_up_properties(cls):
    """Fix up the properties by calling their _fix_up() method.
    Note: This is called by MetaModel, but may also be called manually
    after dynamically updating a model class.
    """