python - {DetachedInstanceError} 父实例 未绑定(bind)到 session ；属性 'owner' 的延迟加载操作无法继续

Question

我收到错误消息:{DetachedInstanceError} 父实例未绑定(bind)到 session ；属性“所有者”的延迟加载操作无法继续

我的 python 代码:

car_obj = my_query_function()  # get a Car object
owner_name = car_obj.owner.name # here generate error!

我的模型:

class Person(EntityClass):
    attributes = ['id', 'name']

    name = sa.Column(sa.String(250))


class Car(EntityClass):
    attributes = ['id', 'brand', 'color', 'purchase_time', 'owner_id']

    brand = sa.Column(sa.String(250))
    color = sa.Column(sa.String(250))
    purchase_time = sa.Column(sa.String(250))
    owner_id = sa.Column(DBKeyType, sa.ForeignKey(Person.__tablename__ + '.id'), nullable=False)
    owner = relationship('Person', cascade='all, delete-orphan', backref=backref('car', cascade='delete'), single_parent=True)

这个是不是跟Car和User的lazy-loading关系设置有关(多对一关联)？我该如何修复关系？提前致谢。

Answer 1

我跟踪文档并通过添加 lazy='subquery' 使其工作

owner = relationship('Person', lazy='subquery', cascade='all, delete-orphan', backref=backref('car', cascade='delete'), single_parent=True)

http://docs.sqlalchemy.org/en/rel_0_9/orm/join_conditions.html