Question

我有两个实体（事件和用户）。每个用户都有几个事件，但我不希望它们存储在StructuredProperty中，因为将来应该可以有多个创建者/管理员。现在我遇到了问题，用户需要事件类进行定义，反之亦然。我该如何实现预期的结构？

两种相互关系的模型。

class Event(EndpointsModel):
    _message_fields_schema = ("id", "name", "creator", 
                        "datetime", "place", "category", "participants")
    creator = ndb.KeyProperty(kind=User)
    participants = ndb.KeyProperty(kind=User, repeated=True)
    name = ndb.StringProperty()
    datetime = ndb.DateTimeProperty(auto_now_add=True)
    place = ndb.GeoPtProperty()
    category = ndb.StringProperty(choices=('all', 'drinking'))

class User(EndpointsModel):

    _message_fields_schema = ("id", "name", "password", "events")

    name = ndb.StringProperty()
    password = ndb.StringProperty()
    events = ndb.KeyProperty(kind=Event, repeated=True)

    def create_event(self, e_name, e_datetime, e_place, e_category):
        event = Event(name=e_name, creator = self.key, datetime=e_datetime, place=e_place, category=e_category)
        event.put()
        self.events.append(event)
        self.put()

    def get_events(self):
        return ndb.get_multi(self.events)

错误讯息：

NameError：名称'User'未定义

编辑1： 我将类型更改为包含类名的字符串，就像Greg建议的那样。但它也不起作用。

class Category(EndpointsModel):
    _message_fields_schema = ("id", "name", "parent")
    name = ndb.StringProperty()
    parent = ndb.KeyProperty(kind='Category', default=None)

class Event(EndpointsModel):

    _message_fields_schema = ("id", "name", "creator", "datetime", 
                               "place", "category")

    participants = ndb.KeyProperty(kind='User', repeated=True)
    creator = ndb.KeyProperty(kind='User')
    name = ndb.StringProperty()
    datetime = ndb.DateTimeProperty(auto_now_add=True)
    place = ndb.GeoPtProperty()
    category = ndb.KeyProperty(Category)

class User(EndpointsModel):

    _message_fields_schema = ("id", "name", "password")

    name = ndb.StringProperty()
    password = ndb.StringProperty()
    events = ndb.KeyProperty(Event, repeated=True)

现在我收到以下堆栈跟踪：

ERROR    2014-01-21 09:38:39,764 service.py:191] Encountered unexpected error from ProtoRPC method implementation: BadValueError (Expected Key, got [])
Traceback (most recent call last):
  File "/home/chris/Downloads/google_appengine/lib/protorpc-1.0/protorpc/wsgi/service.py", line 181, in protorpc_service_app
    response = method(instance, request)
  File "/home/chris/Downloads/google_appengine/lib/endpoints-1.0/endpoints/api_config.py", line 1321, in invoke_remote
    return remote_method(service_instance, request)
[...]
    value = self._call_shallow_validation(value)
  File "/home/chris/Downloads/google_appengine/google/appengine/ext/ndb/model.py", line 1227, in _call_shallow_validation
    return call(value)
  File "/home/chris/Downloads/google_appengine/google/appengine/ext/ndb/model.py", line 1274, in call
    newvalue = method(self, value)
  File "/home/chris/Downloads/google_appengine/google/appengine/ext/ndb/model.py", line 1927, in _validate
    raise datastore_errors.BadValueError('Expected Key, got %r' % (value,))
BadValueError: Expected Key, got []

Answer 1

您可以在KeyProperty构造函数中使用字符串来引用没有模型定义的类型：

class Event(ndb.Model):
  participants = ndb.KeyProperty(kind='User', repeated=True)

Answer 2

您无法创建对实体的此类引用。这是somo解决方案： 1.必须为Event.creator使用普通的StringProperty或者为User实例使用其他id 2.从类User中删除evens - 您可以通过类Events上的索引达到均衡 3.使用第三个实体模型：

class EventCreator(EndpointsModel):
    creator = ndb.KeyProperty(kind=User)
    event =  ndb.KeyProperty(kind=Event)

并从课程用户删除创作者＆amp;来自班级活动删除

Answer 3

您可以在没有kind参数的情况下指定键属性（它是可选的），然后在构造函数或预置挂钩或类似的东西中进行手动检查 - 或者甚至不用担心这种类型：

class Event(EndpointsModel):
    creator = ndb.KeyProperty()

    # Constructor option
    def __init__(self, *args, **kwargs):
        super(Event, self).__init__(*args, **kwargs)
        if 'creator' in kwargs and kwargs['creator'] != 'User':
            raise Exception('oh no')

    # Hook option
    _pre_put_hook(self):
        if self.creator and self.creator.kind() != 'User':
            raise Exception("oh no")

实际语法可能略有不同。随意编辑。

如何在ndb.Models中解决某种鸡蛋关系？

3 个答案: