SQLAlchemy如何检查对象是否在模型中

Question

我希望能够像这样向事件中添加被邀请者：

e = events.get(1)
u = users.get(1)
e.invitees.append(u)

然后在我的服务层中，我想要有一个类似于以下函数的功能：

def add_invitee(self, event, user):
    if user in self.get(event).invitees:
        raise OroposError(u'User already invited')
    event.invitees.append(user)
    return self.save(event), user

我尝试过这个方法，出现了一些问题。当我尝试使用我的函数时，会出现以下错误：

InterfaceError:（InterfaceError）绑定参数0时出错-可能是不支持的类型。u'SELECT events.id AS events_id, events.user_id AS events_user_id, events.event_name AS events_event_name, events.event_mesg AS events_event_mesg, events.start_date AS events_start_date, events.end_date AS events_end_date, events.event_status AS events_event_status, events.rsvp AS events_rsvp, events.created AS events_created \nFROM events \nWHERE events.id = ?' (,)

当我尝试使用e.invitees.append(u)时，会出现以下错误：

  File "/Users/f/.virtualenvs/Oropos/lib/python2.7/site-packages/sqlalchemy/orm/collections.py", line 1057, in append
    item = __set(self, item, _sa_initiator)
  File "/Users/f/.virtualenvs/Oropos/lib/python2.7/site-packages/sqlalchemy/orm/collections.py", line 1029, in __set
    item = getattr(executor, 'fire_append_event')(item, _sa_initiator)
  File "/Users/f/.virtualenvs/Oropos/lib/python2.7/site-packages/sqlalchemy/orm/collections.py", line 733, in fire_append_event
    item, initiator)
  File "/Users/f/.virtualenvs/Oropos/lib/python2.7/site-packages/sqlalchemy/orm/attributes.py", line 910, in fire_append_event
    value = fn(state, value, initiator or self)
  File "/Users/f/.virtualenvs/Oropos/lib/python2.7/site-packages/sqlalchemy/orm/attributes.py", line 1140, in emit_backref_from_collection_append_event
    child_impl = child_state.manager[key].impl
KeyError: 'event'

这个问题困扰了我一段时间。有任何建议吗？

以下是与我的问题相关的模型。

class EventJsonSerializer(JsonSerializer):
    pass


class Event(EventJsonSerializer, db.Model):
    __tablename__ = 'events'

    id = db.Column(db.Integer, primary_key=True)
    user_id = db.Column(db.Integer, db.ForeignKey('users.id'))
    event_name = db.Column(db.String(30))
    event_mesg = db.Column(db.Text)
    start_date = db.Column(db.Date)
    end_date = db.Column(db.Date)
    event_status = db.Column(db.Boolean)
    rsvp = db.Column(db.Date)
    created = db.Column(db.DateTime, default=get_current_time)

    invitees = db.relationship('Invite', backref=db.backref('event'))
    proposals = db.relationship('Proposal', backref=db.backref('event'))


class InviteJsonSerializer(JsonSerializer):
    pass


class Invite(InviteJsonSerializer, db.Model):
    __tablename__ = 'invites'

    id = db.Column(db.Integer, primary_key=True)
    created = db.Column(db.Date, default=get_current_time)
    user_id = db.Column(db.ForeignKey('users.id'))
    event_id = db.Column(db.ForeignKey('events.id'))

    user = db.relationship('User', foreign_keys='Invite.user_id', lazy='joined')


class ProposalJsonSerializer(JsonSerializer):
    pass


class Proposal(ProposalJsonSerializer, db.Model):
    __tablename__ = 'proposals'

    id = db.Column(db.Integer, primary_key=True)
    created = db.Column(db.Date, default=get_current_time)
    date = db.Column(db.Date)
    user_id = db.Column(db.ForeignKey('users.id'))
    event_id = db.Column(db.ForeignKey('events.id'))

- Ptrkcon

Answer 1

如果我没有理解错的话，您正在尝试将一个User实例添加到Invite实例的列表中，您确定这是正确的吗？

根据您的代码，e.invitees包含了具有外键event_id指向e实例的Invite实例。如果您希望invitees表示与User表的多对多关系（这意味着其中有两个外键），您可能需要将其转换为联合表。此外，我敢猜测一个User只能有一个Event的Invite，这意味着这些字段应与UniqueConstraint表参数相关联。

- Berislav Lopac