sqlalchemy - 同一张表的两个不同字段与不同表的一对一关系

Question

我遇到了这个问题：我有两张桌子，一张名为 Team，另一张名为 Event。问题是，我想在这两个表之间建立一对一的关系，但是，在 Event 表中，我想在两个字段中建立这种关系，一个称为 home（用于主队），另一个称为 away（从客场）球队。

但是，sqlalchemy 抱怨我做错了什么，我不知道它是什么，错误是：«ArgumentError: Error created backref 'Event' on relationship 'Event.away_team': property of that名称存在于映射器'Mapper|Team|bt_team'»上。我可能做错了什么？这是我的模型：

#!/usr/bin/env python2
# coding: utf-8
#                        VENI, SANCTE SPIRITUS

import sqlalchemy
import common_models
import datetime


class Team(common_models.Base):

    """ Database table for soccer teams
    """
    __tablename__ = "bt_team"
    id = sqlalchemy.Column(sqlalchemy.Integer, primary_key=True)
    name = sqlalchemy.Column(sqlalchemy.String(30), unique=True)
    monitored_since = sqlalchemy.Column(
        sqlalchemy.DateTime, default=datetime.datetime.utcnow)

    # Huh, another field is not required?
    event_id = sqlalchemy.Column(
        sqlalchemy.Integer, sqlalchemy.ForeignKey("bt_event.id"))

    def __repr__(self):
        return "<Team {}>".format(self.name)


class Event(common_models.Base):

    """ Database table for the events
    """
    __tablename__ = "bt_event"
    id = sqlalchemy.Column(sqlalchemy.Integer, primary_key=True)
    home_team = sqlalchemy.orm.relationship(
        "Team", uselist=False, backref="Event")
    away_team = sqlalchemy.orm.relationship(
        "Team", uselist=False, backref="Event")
    # the "1" in the bet board
    home_wins = sqlalchemy.Column(sqlalchemy.String(7), nullable=True)
    # the "2" in the bet board
    away_wins = sqlalchemy.Column(sqlalchemy.String(7), nullable=True)
    # the "X" in the bet board
    draw = sqlalchemy.Column(sqlalchemy.String(7), nullable=True)
    # when will this event start? (and any bet can be made)
    event_date = sqlalchemy.Column(sqlalchemy.DateTime, nullable=True)
    # when was the last time this event was scraped?
    updated = sqlalchemy.Column(
        sqlalchemy.DateTime, nullable=True)

    def __repr__(self):
        return "<Event {} v {} ({} UK): 1 {} - X {} - 2 {}>".format(
            self.home_team.name, self.away_team.name,
            self.event_date.strftime("%d %B %H:%M"),
            self.home_wins, self.draw, self.away_wins)

    def get_match_teams(self):
        """ Return a string with the teams names which is the event name
        """
        return "{} v {}".format(self.home_team.name,
                                self.away_team.name)

这是完整的错误：

E
======================================================================
ERROR: Get the bets for the next two soccer plays
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/jorge/coders/PPH/clientes/anton_b/app1-539916/codigo/lib/python2.7/site-packages/nose/case.py", line 267, in setUp
    try_run(self.test, names)
  File "/home/jorge/coders/PPH/clientes/anton_b/app1-539916/codigo/lib/python2.7/site-packages/nose/util.py", line 470, in try_run
    return func()
  File "/home/jorge/coders/PPH/clientes/anton_b/app1-539916/codigo/tests/test_bets.py", line 46, in s
    team1 = betevent_models.Team(name="FK Krasnodar")
  File "<string>", line 2, in __init__
  File "/home/jorge/coders/PPH/clientes/anton_b/app1-539916/codigo/lib/python2.7/site-packages/sqlalchemy/orm/instrumentation.py", line 324, in _new_state_if_none                                                                                                                 
    state = self._state_constructor(instance, self)
  File "/home/jorge/coders/PPH/clientes/anton_b/app1-539916/codigo/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py", line 725, in __get__                                                                                                                               
    obj.__dict__[self.__name__] = result = self.fget(obj)
  File "/home/jorge/coders/PPH/clientes/anton_b/app1-539916/codigo/lib/python2.7/site-packages/sqlalchemy/orm/instrumentation.py", line 158, in _state_constructor                                                                                                                 
    self.dispatch.first_init(self, self.class_)
  File "/home/jorge/coders/PPH/clientes/anton_b/app1-539916/codigo/lib/python2.7/site-packages/sqlalchemy/event/attr.py", line 260, in __call__                                                                                                                                    
    fn(*args, **kw)
  File "/home/jorge/coders/PPH/clientes/anton_b/app1-539916/codigo/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line 2687, in _event_on_first_init                                                                                                                       
    configure_mappers()
  File "/home/jorge/coders/PPH/clientes/anton_b/app1-539916/codigo/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line 2583, in configure_mappers                                                                                                                          
    mapper._post_configure_properties()
  File "/home/jorge/coders/PPH/clientes/anton_b/app1-539916/codigo/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line 1688, in _post_configure_properties                                                                                                                 
    prop.init()
  File "/home/jorge/coders/PPH/clientes/anton_b/app1-539916/codigo/lib/python2.7/site-packages/sqlalchemy/orm/interfaces.py", line 144, in
 init                                                                                                                                    
    self.do_init()
  File "/home/jorge/coders/PPH/clientes/anton_b/app1-539916/codigo/lib/python2.7/site-packages/sqlalchemy/orm/relationships.py", line 1553, in do_init                                                                                                                             
    self._generate_backref()
  File "/home/jorge/coders/PPH/clientes/anton_b/app1-539916/codigo/lib/python2.7/site-packages/sqlalchemy/orm/relationships.py", line 1743, in _generate_backref                                                                                                                   
    (backref_key, self, m))
ArgumentError: Error creating backref 'Event' on relationship 'Event.away_team': property of that name exists on mapper 'Mapper|Team|bt_team'

我怎样才能实现我想要的？

编辑： 似乎更适合建立 多对多 关系，因为团队可以有 N 个事件和一个事件可以有两个团队。

Answer 1

这看起来您的 Event 对象只需要引用两个 Team 对象，这将是两个多对一：

from sqlalchemy import Column, ForeignKey, Integer, String, create_engine
from sqlalchemy.orm import relationship, Session
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()


class Team(Base):
    __tablename__ = 'team'

    id = Column(Integer, primary_key=True)
    name = Column(String)


class Event(Base):
    __tablename__ = 'event'

    id = Column(Integer, primary_key=True)
    home_id = Column(ForeignKey('team.id'))
    away_id = Column(ForeignKey('team.id'))

    home_team = relationship("Team", foreign_keys=home_id)
    away_team = relationship("Team", foreign_keys=away_id)

e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)

sess = Session(e)

t1, t2, t3, t4 = (
    Team(name='t1'), Team(name='t2'),
    Team(name='t3'), Team(name='t4')
)

sess.add_all([t1, t2, t3, t4])

sess.add_all([
    Event(home_team=t1, away_team=t2),
    Event(home_team=t3, away_team=t1),
    Event(home_team=t2, away_team=t4)
])

sess.commit()