python – sqlAlchemy,具体继承,但parent有foreignKey

我有3个班：

>用户
>员工< - DB中不需要
>经理

Manager继承自Employee.用户表与继承无关.

到现在为止还挺好：

class User(Base):
    __tablename__ = 'user'
    id = Column(Integer,primary_key=True)
    email = Column(String(255))

class Employee(AbstractConcreteBase,Base):
    name = Column(String(30))

class Manager(Employee):
    __tablename__ = 'manager'
    employee_id = Column(Integer,primary_key=True)
    dept = Column(String(30))
    __mapper_args__ = {'polymorphic_identity':'manager','concrete':True}

它创建了User和Manager,这就是我想要的.

但,

如果我们在父类中引入ForeignKey,上面会中断：

class Employee(AbstractConcreteBase,Base):
    name = Column(String(30))
    user_id = Column(Integer,ForeignKey('user.id'))

错误是：

sqlalchemy.exc.InvalidRequestError：

Columns with foreign keys to other columns must be declared as @declared_attr callables on declarative mixin classes.

到目前为止,我不明白the mixin docs (link)

在基类中允许外键(在本例中为Employee)需要什么？

解决方法

from sqlalchemy import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.declarative import declared_attr


Base = declarative_base()

class User(Base):
    __tablename__ = 'user'
    id = Column(Integer,primary_key=True)
    email = Column(String(255))

class Employee(object):
    name = Column(String(30))
    @declared_attr
    def user_id(cls):
        return Column(Integer,ForeignKey('user.id'))

class Manager(Base,Employee):
    __tablename__ = 'manager'
    employee_id = Column(Integer,'concrete':True}

ref：Mixing in Columns

（编辑：安卓应用网）

【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容!