我有一个有点分支的关系结构(让我们用一个配对数据库的例子-不幸的是,实际情况有点复杂):
class Hobby(Base):
__tablename__ = 'hobby'
id = Column(Integer, primary_key=True)
hobby_name = Column(String(255, u'utf8_unicode_ci'), nullable=False)
class Guy(Base):
__tablename__ = 'guy'
id = Column(Integer, primary_key=True)
name = Column(String(255, u'utf8_unicode_ci'), nullable=False)
class Girl(Base):
__tablename__ = 'girl'
id = Column(Integer, primary_key=True)
name = Column(String(255, u'utf8_unicode_ci'), nullable=False)
class Match(Base):
__tablename__ = 'match'
id = Column(Integer, primary_key=True)
guy_id = Column(ForeignKey(u'guy.id'), nullable=False)
girl_id = Column(ForeignKey(u'girl.id'), nullable=False)
guy = relationship(u'Guy', backref = 'matches')
girl = relationship(u'Girl', backref = 'matches')
class GuyHobbies(Base):
__tablename__ = 'guy_hobbies'
id = Column(Integer, primary_key=True)
guy_id = Column(ForeignKey(u'guy.id'), nullable=False)
hobby_id = Column(ForeignKey(u'hobby.id'), nullable=False)
guy = relationship(u'Guy', backref = 'hobbies')
hobby = relationship(u'Hobby', backref = 'guys')
class GirlHobbies(Base):
__tablename__ = 'girl_hobbies'
id = Column(Integer, primary_key=True)
girl_id = Column(ForeignKey(u'girl.id'), nullable=False)
hobby_id = Column(ForeignKey(u'hobby.id'), nullable=False)
girl = relationship(u'Girl', backref = 'hobbies')
hobby = relationship(u'Hobby', backref = 'girls')
我现在想在GirlHobby和GuyHobby之间建立一个连接,它考虑了通过Hobby和通过Match建立的关系。也就是说,我正在做一个
matched_hobbies = session.query(GuyHobbies).join(GuyHobbies.guy).\
join(GuyHobbies.hobby).join(Guy.matches).\
join(Match.girl).outerjoin(Girl.hobbies).all()
但是,生成的查询缺少下面标记的部分。如何让SQLAlchemy添加此条件?你知道吗
SELECT guy_hobbies.id AS guy_hobbies_id, guy_hobbies.guy_id AS guy_hobbies_guy_id,
guy_hobbies.hobby_id AS guy_hobbies_hobby_id
FROM guy_hobbies INNER JOIN guy ON guy.id = guy_hobbies.guy_id
INNER JOIN hobby ON hobby.id = guy_hobbies.hobby_id
INNER JOIN `match` ON guy.id = `match`.guy_id
INNER JOIN girl ON girl.id = `match`.girl_id
LEFT OUTER JOIN girl_hobbies ON girl.id = girl_hobbies.girl_id
#MISSING: AND hobby.id = girl_hobbies.hobby_id
另外:我试图建立一个直接的关系,男性嗜好和女孩之间的使用
girl_hobbies = relationship('GirlHobbies',
primaryjoin ="and_(GuyHobbies.guy_id == Guy.id,
Match.guy_id == Guy.id ,Match.girl_id == Girl.id,
GirlHobbies.girl_id == Girl.id ,
GirlHobbies.hobby_id == Hobby.id,
GuyHobbies.hobby_id == Hobby.id)")
但我得到了一个颇具讽刺意味的错误信息:
Could not locate any simple equality expressions involving locally mapped foreign key columns for primary join condition 'guy_hobbies.guy_id = guy.id AND match.guy_id = guy.id AND match.girl_id = girl.id AND girl_hobbies.girl_id = girl.id AND girl_hobbies.hobby_id = hobby.id AND guy_hobbies.hobby_id = hobby.id' on relationship GuyHobbies.girl_hobbies.
它正好显示了我希望SQLAlchemy使用的连接条件。。。你知道吗
由于所有的积分都在SQLAlchemy IRC通道的@inklesspen中,连接条件必须直接在连接中指定,即
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