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我正在使用谷歌应用程序引擎/ python。我创建了一个自定义的数据类型和属性。但我有使用它的问题。这是我的定义在Google App Engine中使用自定义属性
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()
,这是我如何使用它:
obj = MyClass(date=MyDateTime(2011,1,1))
obj.put()
,我得到了以下错误消息:
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'>
我搜索解决方案一段时间并不能解决它。如果有人知道如何解决它,请提前致谢。
感谢您的回答。我想通了,首要的问题是,自定义数据类型不能进入数据存储,所以我需要/从平常使用的数据类型和get_value_for_datastore
make_value_from_datastore
这是我修改的属性定义来包装/解包自定义数据类型:
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)
的关键是,使用get_value_for datastore
改变一个不可存储MyDateTime对象为可存储日期时间对象,make_value_from_datastore
反之亦然。
如果这是真实的代码而不是演示,您可以考虑在模板过滤器中处理日期格式,而不是定制属性。 –
我同意德鲁 - 这是很多箍环,只是为了在'str'上获得自定义行为。 –