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{DetachedInstanceError} The parent <Car> instance is not attached to the session; lazy loading of the "owner" attribute cannot continue

I got an error message: {DetachedInstanceError} The parent instance is not attached to the session; lazy loading of the "owner" attribute cannot continue

My python code:

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

My model:

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)

Does it have something to do with establishing a lazy loading relationship between Car and User (a one-to-one association)? How can I fix my relationship? Thanks in advance.

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2 answers


I traced the docs and did this by adding lazy='subquery' 

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

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Did the job by adding joinedload_all()

in session.query(Car).options()

, for example:

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


luck

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