SQL Alchemy奇怪的行为从同一个表中加入多个列

Posted 2023-03-23

【中文标题】SQL Alchemy奇怪的行为从同一个表中加入多个列

【英文标题】：SQL Alchemy Strange behaviour Join Multiple Columns from same table

【发布时间】：2016-04-15 21:09:18

【问题描述】：

我正在尝试执行一个查询，该查询涉及连接同一列中的两列。

这些是我的模型：

class Match(Base):
    __tablename__ = 'matches'

    id = Column(Integer, primary_key=True)
    date = Column(Date, nullable=False)
    time = Column(Time, nullable=True)
    league_id = Column(ForeignKey('leagues.id'), nullable=False, index=True)
    league = relationship('League', backref='matches')
    type = Column(enums.matches_types)
    home_id = Column(ForeignKey('teams.id'), nullable=False, index=True)
    home = relationship('Team', foreign_keys=[home_id], backref='home_matches')
    away_id = Column(ForeignKey('teams.id'), nullable=False, index=True)
    away = relationship('Team', foreign_keys=[away_id], backref='away_matches')


class Team(Base):
    __tablename__ = 'teams'

    id = Column(Integer, primary_key=True)
    name = Column(String, nullable=False)
    country_id = Column(ForeignKey('countries.id'), nullable=False, index=True)
    country = relationship('Country', backref='teams')

这是我在 SQLAlchemy 中写的：

self.db_match = Session.query(Match).join(home, Match.home).options(contains_eager(Match.home)
                        ).join(away, Match.away).options(contains_eager(Match.away)
                        ).join(Match.b_reference).options(contains_eager(Match.b_reference)
                        ).filter(home.name == self.match['home']['name']
                        ).filter(away.name == self.match['away']['name']
                        ).filter(Match.date == self.match['date'])

SQLAlchemy 对纯 SQL 的翻译如下：

SELECT teams_1.name, teams_2.name, matches.id, matches_b_reference_codes.code
FROM teams, matches JOIN teams AS teams_1 ON teams_1.id = matches.home_id 
JOIN teams AS teams_2 ON teams_2.id = matches.away_id 
JOIN matches_b_reference_codes ON matches.id = matches_b_reference_codes.match_id 
WHERE teams_1.name = 'Portland Trail Blazers' AND teams_2.name = 'Miami Heat' AND matches.date = '2011-01-09';

但这正是我需要的：

SELECT teams_1.name, teams_2.name, matches.id, matches_b_reference_codes.code
**FROM matches JOIN teams AS teams_1 ON teams_1.id = matches.home_id** 
JOIN teams AS teams_2 ON teams_2.id = matches.away_id 
JOIN matches_b_reference_codes ON matches.id = matches_b_reference_codes.match_id 
WHERE teams_1.name = 'Portland Trail Blazers' AND teams_2.name = 'Miami Heat' AND matches.date = '2011-01-09';

【问题讨论】：

什么是home，什么是away？ Match.home 和 Match.away 是什么？

抱歉，模型出现错误。我更正了。

【参考方案1】：

您错误地使用了contains_eager。加入别名时需要指定alias 参数：

home = aliased(Team)
away = aliased(Away)
Session.query(Match).join(home, Match.home) \
                    .options(contains_eager(Match.home, alias=home)) \
                    .join(away, Match.away) \
                    .options(contains_eager(Match.away, alias=away)) \
                    ... \
                    .filter(...)