SQLAlchemy：单表继承，子级中的同一列

Question

我目前使用单表继承策略映射类层次结构（我无法使用joind）。该层次结构可能如下所示：class Parent(Base):    __tablename__ = 'mytable'    __mapper_args__ = {        'polymorphic_on' : type,        'polymorphic_identity' : 'parent'    }    id = Column(Integer, primary_key = True)    type = Column(String(32), nullable = False)class Child1(Parent):    __mapper_args__ = { 'polymorphic_identity' : 'child1' }    property1 = Column(Integer)class Child2(Parent):    __mapper_args__ = { 'polymorphic_identity' : 'child2' }    property1 = Column(Integer)class Child3(Parent):    __mapper_args__ = { 'polymorphic_identity' : 'child3' }    other_property = Column(Integer)那么问题是，我想有一property1两个Child1和Child2，但不是Child3。上面的当前代码导致错误：sqlalchemy.exc.ArgumentError: Column 'property1' on class <class'__main__.Child2'>  conflicts with existing column 'mytable.property1'我当然可以添加其他层的继承层次这Child1与Child2从派生，并包含property1列，但Child1和Child2几乎不相互关联的，但我想重用这两个类相同的数据库列。我已经尝试添加property1 = Child1.property1到，Child2但没有成功（实例值未存储在的数据库中Child2）谁能指出如何重用另一个子类已定义的列？

Answer 1

直接根据解决列冲突中的文档进行改编：

from sqlalchemy import *

from sqlalchemy.orm import *

from sqlalchemy.ext.declarative import declarative_base, declared_attr

Base = declarative_base()

class Parent(Base):

    __tablename__ = 'mytable'

    id = Column(Integer, primary_key = True)

    type = Column(String(32), nullable = False)

    __mapper_args__ = {

        'polymorphic_on' : type,

        'polymorphic_identity' : 'parent'

    }

class Child1(Parent):

    __mapper_args__ = { 'polymorphic_identity' : 'child1' }

    @declared_attr

    def property1(cls):

        return Parent.__table__.c.get('property1', Column(Integer))

class Child2(Parent):

    __mapper_args__ = { 'polymorphic_identity' : 'child2' }

    @declared_attr

    def property1(cls):

        return Parent.__table__.c.get('property1', Column(Integer))

class Child3(Parent):

    __mapper_args__ = { 'polymorphic_identity' : 'child3' }

    other_property = Column(Integer)

e = create_engine("sqlite://", echo=True)

Base.metadata.create_all(e)

s = Session(e)

s.add_all([Child1(property1=1), Child2(property1=2), Child3(other_property=3)])

s.commit()

for p in s.query(Parent):

    if isinstance(p, (Child1, Child2)):

        print p.property1

    elif isinstance(p, Child3):

        print p.other_property