SQLAlchemy将多个外键在一个映射类中转换为相同的主键

Question

我试图设置一个postgresql表,它有两个指向另一个表中相同主键的外键.

当我运行脚本时,我收到错误

sqlalchemy.exc.AmbiguousForeignKeysError:无法确定关系Company.stakeholder上的父/子表之间的连接条件 - 有多个链接表的外键路径.指定'foreign_keys'参数,提供应列为包含对父表的外键引用的列的列表.

这是SQLAlchemy文档中的确切错误,但当我复制它们提供的解决方案时,错误不会消失.我能做错什么？

#The business case here is that a company can be a stakeholder in another company.
class Company(Base):
    __tablename__ = 'company'
    id = Column(Integer, primary_key=True)
    name = Column(String(50), nullable=False)

class Stakeholder(Base):
    __tablename__ = 'stakeholder'
    id = Column(Integer, primary_key=True)
    company_id = Column(Integer, ForeignKey('company.id'), nullable=False)
    stakeholder_id = Column(Integer, ForeignKey('company.id'), nullable=False)
    company = relationship("Company", foreign_keys='company_id')
    stakeholder = relationship("Company", foreign_keys='stakeholder_id')

我在这里看到过类似的问题,但有些答案建议人们primaryjoin在文档中使用a 表明你primaryjoin在这种情况下不需要.

Answer 1

尝试从foreign_keys中删除引号并将其作为列表.从官方文档Relationship Configuration: Handling Multiple Join Paths

在版本0.8中更改:relationship()可以foreign_keys仅根据参数解决外键目标之间的歧义; 该primaryjoin参数不再需要在这种情况下.

下面的自包含代码适用于sqlalchemy>=0.9:

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

engine = create_engine(u'sqlite:///:memory:', echo=True)
session = scoped_session(sessionmaker(bind=engine))
Base = declarative_base()

#The business case here is that a company can be a stakeholder in another company.
class Company(Base):
    __tablename__ = 'company'
    id = Column(Integer, primary_key=True)
    name = Column(String(50), nullable=False)

class Stakeholder(Base):
    __tablename__ = 'stakeholder'
    id = Column(Integer, primary_key=True)
    company_id = Column(Integer, ForeignKey('company.id'), nullable=False)
    stakeholder_id = Column(Integer, ForeignKey('company.id'), nullable=False)
    company = relationship("Company", foreign_keys=[company_id])
    stakeholder = relationship("Company", foreign_keys=[stakeholder_id])

Base.metadata.create_all(engine)

# simple query test
q1 = session.query(Company).all()
q2 = session.query(Stakeholder).all()

Answer 2

最新文档：

• http://docs.sqlalchemy.org/en/latest/orm/join_conditions.html#handling-multiple-join-paths

foreign_keys=文档中的形式产生了一个 NameError，不确定在类尚未创建时它是如何工作的。通过一些黑客攻击，我能够成功：

company_id = Column(Integer, ForeignKey('company.id'), nullable=False)
company = relationship("Company", foreign_keys='Stakeholder.company_id')

stakeholder_id = Column(Integer, ForeignKey('company.id'), nullable=False)
stakeholder = relationship("Company",
                            foreign_keys='Stakeholder.stakeholder_id')

换句话说：

… foreign_keys='CurrentClass.thing_id')