我如何引用外键表两次？ [英] How do I refer to a foreign key table twice?

问题描述

u'detail'：u一个或多个映射器初始化失败 - 无法继续
与其他映射器的初始化。原始异常是：可能
不能确定
关系上的父/子表之间的连接条件Vote.user - 有多个外键路径链接
tables。指定'foreign_keys'参数，提供
列表，这些列应被计算为包含对父表的外键
引用。

表 A 被定义为：

  class User（postgres.Model）：
 
 def __init __（self，
 name 
）：
 self.name = name 
 
 id = postgres.Column（postgres.Integer，primary_key = True，autoincrement = True）
 name = postgres.Column（postgres.String（32），nullable = False，unique = True）
  

Tab le B 被定义为：

  class Vote（postgres.Model ）：
 
 def __init __（self，
 user_id，
 responder_id，
 #timestamp_request，
 #timestamp_respond，
 value 
 ）：
 self.user_id = user_id 
 self.responder_id = responder_id 
＃self.timestamp_request = timestamp_request 
＃self.timestamp_respond = timestamp_respond 
 self.value = value 
 
 id = postgres.Column（postgres.Integer，primary_key = True，autoincrement = True）
 user_id = postgres.Column（postgres.Integer，postgres.ForeignKey（'user.id'）） 
 user = postgres.relationship（User，backref = postgres.backref（'votes_user'））
 responder_id = postgres.Column（postgres.Integer，postgres.ForeignKey（'user.id'））
 responder = postgres.relationship（User，backref = postgres.backref（'votes_responder'））
 timestamp_request = p ostgres.Column（postgres.DateTime，default = datetime.datetime.utcnow，nullable = False，unique = False）
 timestamp_respond = postgres.Column（postgres.DateTime，default = datetime.datetime.utcnow，onupdate = datetime。 datetime.utcnow，nullable = False，unique = False）
 value = postgres.Column（postgres.Enum（'up'，'down'，name ='vote_value_enum'），nullable = True）
  

解决方案

SQLAlchemy无法找到关系路径。 b

  user_id = Column（ForeignKey（'user.id'））
 user = relationship（User，backref = backref（'votes_user'））
 responder_id = Column（ForeignKey（'user.id'））
 responder = relationship（User，backref = backref（'votes_responder'））
  

$ b $ p responder 关系必须使用 responder_id 或 USER_ID ？我知道这很明显，但SQLAlchemy在这里不考虑列名。您可以将 responder_id 重命名为 foobar ，这样做没有任何区别。

$ p $ user = relationship（User，foreign_keys = [ user_id]，backref = backref（'votes_user'））
responder = relationship（User，foreign_keys = [responder_id]，backref = backref（'votes_responder'））
pre>

I get the following error:

u'detail': u"One or more mappers failed to initialize - can't proceed with initialization of other mappers. Original exception was: Could not determine join condition between parent/child tables on relationship Vote.user - there are multiple foreign key paths linking the tables. Specify the 'foreign_keys' argument, providing a list of those columns which should be counted as containing a foreign key reference to the parent table."

Table A is being defined as:

class User(postgres.Model):

    def __init__(self,
        name
    ):
        self.name = name

    id = postgres.Column(postgres.Integer , primary_key=True , autoincrement=True)
    name = postgres.Column(postgres.String(32) , nullable=False , unique=True)

Table B is being defined as:

class Vote(postgres.Model):

    def __init__(self,
        user_id,
        responder_id,
        #timestamp_request,
        #timestamp_respond,
        value 
    ):
        self.user_id = user_id
        self.responder_id = responder_id
        #self.timestamp_request = timestamp_request
        #self.timestamp_respond = timestamp_respond
        self.value = value

    id = postgres.Column(postgres.Integer , primary_key=True , autoincrement=True)
    user_id = postgres.Column(postgres.Integer , postgres.ForeignKey('user.id'))
    user = postgres.relationship(User , backref=postgres.backref('votes_user'))
    responder_id = postgres.Column(postgres.Integer , postgres.ForeignKey('user.id'))
    responder = postgres.relationship(User , backref=postgres.backref('votes_responder'))
    timestamp_request = postgres.Column(postgres.DateTime , default=datetime.datetime.utcnow , nullable=False , unique=False)
    timestamp_respond = postgres.Column(postgres.DateTime , default=datetime.datetime.utcnow , onupdate=datetime.datetime.utcnow , nullable=False , unique=False)
    value = postgres.Column(postgres.Enum('up' , 'down' , name='vote_value_enum') , nullable=True)

解决方案

SQLAlchemy is unable to discover the relationship path.

user_id = Column(ForeignKey('user.id'))
user = relationship(User, backref=backref('votes_user'))
responder_id = Column(ForeignKey('user.id'))
responder = relationship(User, backref=backref('votes_responder'))

Do the responder relationship must join using responder_id or user_id? I know it is obvious to us, but SQLAlchemy don't consider column names here. You can rename responder_id as foobar and it'll make no difference.

Define the foreign keys you want to use for each relationship.

user = relationship(User, foreign_keys=[user_id], backref=backref('votes_user'))
responder = relationship(User, foreign_keys=[responder_id], backref=backref('votes_responder'))

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