Question

我正在尝试在Toy.owner关系上加载一个值。这些是我的模特：

class User(db.Model):
    __tablename__ = 'User'
    id = db.Column(db.Integer, primary_key=True)
    type = db.Column(db.String(50))
    nickname = db.Column(db.String(255))
    email = db.Column(db.String(255))
    password = db.Column(db.String(255))

    __mapper_args__ = {
        "polymorphic_on":type,
        'polymorphic_identity':'user',
        'with_polymorphic':'*'
    }

class Owner(User):
    __tablename__ = 'Owner'
    id = db.Column(db.Integer, db.ForeignKey('User.id', ondelete='CASCADE'), primary_key=True)
    owner_id = db.Column(db.Integer, autoincrement=True, primary_key=True, unique=True)  
    toys = db.relationship('Toy', backref='owner', lazy='dynamic')

    __mapper_args__ = {'polymorphic_identity':'owner'}

class Toy(db.Model):
    __tablename__ = 'Toy'
    id = db.Column(db.Integer, primary_key=True)
    owner_id = db.Column(db.Integer, db.ForeignKey('Owner.owner_id'))

此视图应使用clicked_toy.owner_id：

@app.route('/<path:toy_id>', methods=['GET','POST'])
def toy_info(toy_id):
    clicked_toy = db.session.query(Toy).filter(Toy.id == toy_id).first()
    owner = db.session.query(Owner).filter(Owner.owner_id == clicked_toy.owner.owner_id).first()
    return render_template('toy_info.html', clicked_toy=clicked_toy, owner=owner)

这不起作用，我收到了错误：

File ".../controller.py", line 67, in toy_info
owner = db.session.query(Owner).filter(Owner.owner_id == clicked_toy.owner.owner_id).first()
AttributeError: 'NoneType' object has no attribute 'owner'

当我尝试拨打clicked_toy.owner_id时，我收到同样的错误：

 File ".../controller.py", line 67, in toy_info
 owner = db.session.query(Owner).filter(Owner.owner_id == clicked_toy.owner_id).first()
 AttributeError: 'NoneType' object has no attribute 'owner_id'

我缺少什么，我该如何解决？

Answer 1

如果没有结果，

.first()会返回None。因此，您对clicked_toy的查询未返回任何结果。

当你所做的只是过滤主键时，你可以使用get而不是filter。如果没有结果，Flask-SQLAlchemy更进一步允许你加注404。

clicked_toy = Toy.query.get_or_404(toy_id)

＆＃39; NoneType＆＃39;对象没有属性＆＃39; owner＆＃39;当试图访问关系

1 个答案: