Question

我想为我的app引擎应用实现一个简单的VersionedModel基础模型类。我正在寻找一种不涉及明确选择要复制的字段的模式。

我正在尝试这样的东西，但这是为了我的口味，并没有在生产环境中测试它。

class VersionedModel(BaseModel):
    is_history_copy     = db.BooleanProperty(default=False)
    version             = db.IntegerProperty()
    created             = db.DateTimeProperty(auto_now_add=True)
    edited              = db.DateTimeProperty()
    user                = db.UserProperty(auto_current_user=True)

    def put(self, **kwargs):
        if self.is_history_copy:
            if self.is_saved():
                raise Exception, "History copies of %s are not allowed to change" % type(self).__name__
            return super(VersionedModel, self).put(**kwargs)
        if self.version is None:
            self.version = 1
        else:
            self.version = self.version +1
        self.edited =  datetime.now() # auto_now would also affect copies making them out of sync
        history_copy = copy.copy(self)
        history_copy.is_history_copy = True
        history_copy._key = None
        history_copy._key_name = None
        history_copy._entity = None
        history_copy._parent = self
        def tx():
            result = super(VersionedModel, self).put(**kwargs)
            history_copy._parent_key = self.key()
            history_copy.put()
            return result
        return db.run_in_transaction(tx)

有没有人有更简洁的清洁解决方案来保存应用引擎模型的版本历史记录？

编辑：将copy移出tx。感谢@Adam Crossland的建议。

Answer 1

查看Model类的properties静态方法。有了这个，您可以获得一个属性列表，并使用它来获取它们的值，如下所示：

  @classmethod
  def clone(cls, other, **kwargs):
    """Clones another entity."""
    klass = other.__class__
    properties = other.properties().items()
    kwargs.update((k, p.__get__(other, klass)) for k, p in properties)
    return cls(**kwargs)

如何浅层复制app引擎模型实例来创建新实例？

1 个答案: