Question

我正在使用谷歌应用引擎/ python。我已经创建了一个自定义数据类型和属性。但我使用它有问题。这是我的定义

from datetime import datetime

class MyDateTime(datetime):
    def __str__(self):
        return self.strftime("%Y-%m-%d %H:%M")

class MyDateTimeProperty(db.Property):
    # specify datatype
    data_type = MyDateTime

    # For writing to datastore.
    def get_value_for_datastore(self, model_instance):
        return super(MyDateTimeProperty, self).get_value_for_datastore(model_instance)

    # For reading from datastore.
    def make_value_from_datastore(self, value):
        return super(MyDateTimeProperty, self).validate(value)

class MyClass(db.Model):
    date = MyDateTimeProperty()

这就是我使用它的方式：

obj = MyClass(date=MyDateTime(2011,1,1))
obj.put()

我收到以下错误消息：

Traceback (most recent call last):
  File "C:\Program Files\Google\google_appengine\google\appengine\ext\admin\__init__.py", line 295, in post
    exec(compiled_code, globals())
  File "<string>", line 23, in <module>
  File "C:\Program Files\Google\google_appengine\google\appengine\ext\db\__init__.py", line 1052, in put
    self._populate_internal_entity()
  File "C:\Program Files\Google\google_appengine\google\appengine\ext\db\__init__.py", line 1020, in _populate_internal_entity
    self._entity = self._populate_entity(_entity_class=_entity_class)
  File "C:\Program Files\Google\google_appengine\google\appengine\ext\db\__init__.py", line 1092, in _populate_entity
    self._to_entity(entity)
  File "C:\Program Files\Google\google_appengine\google\appengine\ext\db\__init__.py", line 1005, in _to_entity
    self.__set_property(entity, prop.name, prop.get_value_for_datastore(self))
  File "C:\Program Files\Google\google_appengine\google\appengine\ext\db\__init__.py", line 995, in __set_property
    entity[name] = datastore_value
  File "C:\Program Files\Google\google_appengine\google\appengine\api\datastore.py", line 881, in __setitem__
    datastore_types.ValidateProperty(name, value)
  File "C:\Program Files\Google\google_appengine\google\appengine\api\datastore_types.py", line 1477, in ValidateProperty
    'Unsupported type for property %s: %s' % (name, v.__class__))
BadValueError: Unsupported type for property date: <class '__main__.MyDateTime'>

我已经搜索了一段时间的解决方案但无法解决它。如果有人知道如何解决它，请提前致谢。

谢谢你的回答。我发现主要问题是自定义数据类型无法进入数据存储区，因此我需要使用get_value_for_datastore和make_value_from_datastore

将自定义数据类型打包/解包到常规数据类型中

这是我修改后的属性定义：

class MyDateTimeProperty(db.Property):
    # specify datatype
    data_type = MyDateTime

    # For writing to datastore.
    def get_value_for_datastore(self, model_instance):
        date = super(MyDateTimeProperty, self).get_value_for_datastore(model_instance)
        return datetime(date.year, date.month, date.day, date.hour, date.minute)

    # For reading from datastore.
    def make_value_from_datastore(self, value):
        if value is None:
            return None
        return MyDateTime(value.year, value.month, value.day, value.hour, value.minute)

关键是，使用get_value_for datastore将不可存储的MyDateTime对象更改为可存储的日期时间对象，然后使用make_value_from_datastore反之亦然。

Answer 1

如果Property子类的数据类型不是默认验证器所知的已定义数据存储数据类型之一，则需要定义validate()子类。 this article中有一个验证方法示例。

在Google App Engine中使用自定义属性

1 个答案: