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
你可以像这样使用mixin：
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