Sqlalchemy、继承与关系

Question

我有一个通用的用户对象，这个对象是我网站的基础类，使用了连接表的方式来构建。


class User(Base):
    __tablename__ = "auth_user"

    id = Column(Integer, primary_key = True)
    username = Column(String(100), nullable = False, unique = True, index = True)
    ...
    type = Column(String(1))
    __mapper_args__ = {'polymorphic_on' : type, "extension" : HashExtension()}

然后我基于这个类创建了一个员工对象。


class Staff(User):
    __tablename__ = "auth_staff"
    __mapper_args__ = {'polymorphic_identity' : 's'}    
    id = Column(Integer, ForeignKey('auth_user.id'), primary_key = True)

现在我又有一个候选人对象，同样是从用户对象派生出来的。


class Candidate(User):
    __tablename__ = "candidates_candidate"
    __mapper_args__ = {'polymorphic_identity' : 'c'}
    id = Column(Integer, ForeignKey('auth_user.id'), primary_key = True)
    ...
    staff_id = Column(Integer, ForeignKey("auth_user.id"), nullable = False)

    staff = relationship("Staff", backref = backref("candidates", order_by = id))

到目前为止，候选人对象的部分都没问题。我想让它能链接回员工对象，但我遇到了关于没有“primaryjoin”的错误，我对这个关系应该如何链接到员工对象感到困惑——是不是应该链接到用户对象，因为员工是从用户派生的呢？……

任何建议我都会非常感激。

~~~~~~~~~更新 2月3日~~~~~~~~~~~~~~

修订后的代码 - 仍然抛出关于primaryjoin的错误。如果我添加了primaryjoin，它还是会出错。


#!/usr/bin/env python
from sqlalchemy import Column, Integer, String, ForeignKey, Boolean
from sqlalchemy.orm import relationship, backref, sessionmaker
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import create_engine

class DomainBase(object):
    active = Column(Boolean, default = True, nullable = False)

    def __str__(self):
        return repr(self)

Base = declarative_base(cls = DomainBase)

class User(Base):
    __tablename__ = "auth_user"

    id = Column(Integer, primary_key = True)
    username = Column(String(100), nullable = False, unique = True, index = True)
    type = Column(String(1))
    __mapper_args__ = {'polymorphic_on' : type}
class Staff(User):
    __tablename__ = "auth_staff"
    __mapper_args__ = {'polymorphic_identity' : 's'}    
    id = Column(Integer, ForeignKey('auth_user.id'), primary_key = True)


class Candidate(User):
    __tablename__ = "candidates_candidate"
    __mapper_args__ = {'polymorphic_identity' : 'c'}
    id = Column(Integer, ForeignKey('auth_user.id'), primary_key = True)
    staff_id = Column(Integer, ForeignKey("auth_staff.id"), nullable = False)

    staff = relationship("Staff", backref = backref("candidates", order_by = id))


engine = create_engine('sqlite:///:memory:')
Base.metadata.create_all(engine)

Session = sessionmaker(bind = engine, autocommit=True)
session = Session()

with session.begin():
    s = Staff(username = "DaveSmith")
    session.add_all([s])

继承 sqlalchemy 关系映射 primaryjoin 连接表用户对象员工对象候选人对象

Sqlalchemy、继承与关系

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