{DetachedInstanceError}父实例<Car>未绑定到会话;属性'owner'的延迟加载操作无法继续

Question

我收到错误消息：{DetachedInstanceError} 父实例未绑定到会话;属性"所有者"的延迟加载操作无法继续

我的蟒蛇代码：

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)

这与 Car 和用户之间的延迟加载关系设置（多对一关联）有关吗？如何修复关系？提前谢谢。

Answer 1

我跟踪了文档并通过添加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

Answer 2

通过在session.query(Car).options()中添加joinedload_all()使其工作，例如：

cars = session.query(Car).options(joinedload_all('*')).all()
session.close()
for car in cars:
     "do your struff"

祝你好运