Question

以下是错误日志当我尝试创建新用户时出现此错误：

u = User (...)

错误日志：

Traceback (most recent call last)
File "/usr/lib/python3.6/site-packages/flask/app.py", line 1994, in __call__
return self.wsgi_app(environ, start_response)
File "/usr/lib/python3.6/site-packages/flask/app.py", line 1985, in wsgi_app
response = self.handle_exception(e)
File "/usr/lib/python3.6/site-packages/flask/app.py", line 1540, in handle_exception
reraise(exc_type, exc_value, tb)
File "/usr/lib/python3.6/site-packages/flask/_compat.py", line 33, in reraise
raise value
File "/usr/lib/python3.6/site-packages/flask/app.py", line 1982, in wsgi_app
response = self.full_dispatch_request()
File "/usr/lib/python3.6/site-packages/flask/app.py", line 1614, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/usr/lib/python3.6/site-packages/flask/app.py", line 1517, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/usr/lib/python3.6/site-packages/flask/_compat.py", line 33, in reraise
raise value
File "/usr/lib/python3.6/site-packages/flask/app.py", line 1612, in full_dispatch_request
rv = self.dispatch_request()
File "/usr/lib/python3.6/site-packages/flask/app.py", line 1598, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "/home/quechon/PycharmProjects/untitled3/myapp/login/routes.py", line 66, in _register_process
timecreated=datetime.datetime.utcnow()
File "<string>", line 4, in __init__

File "/usr/lib/python3.6/site-packages/sqlalchemy/orm/state.py", line 414, in _initialize_instance
manager.dispatch.init_failure(self, args, kwargs)
File "/usr/lib/python3.6/site-packages/sqlalchemy/util/langhelpers.py", line 60, in __exit__
compat.reraise(exc_type, exc_value, exc_tb)
File "/usr/lib/python3.6/site-packages/sqlalchemy/util/compat.py", line 186, in reraise
raise value
File "/usr/lib/python3.6/site-packages/sqlalchemy/orm/state.py", line 411, in _initialize_instance
return manager.original_init(*mixed[1:], **kwargs)
File "/home/quechon/PycharmProjects/untitled3/myapp/models.py", line 80, in __init__
self.follow(self)
File "/home/quechon/PycharmProjects/untitled3/myapp/models.py", line 47, in follow
if not self.is_following(user):
File "/home/quechon/PycharmProjects/untitled3/myapp/models.py", line 57, in is_following
return self.followed.filter_by(followed_id=user.id).first() is not None
File "/usr/lib/python3.6/site-packages/sqlalchemy/orm/query.py", line 1517, in filter_by
return self.filter(sql.and_(*clauses))
File "<string>", line 2, in filter

File "/usr/lib/python3.6/site-packages/sqlalchemy/orm/base.py", line 198, in generate
self = args[0]._clone()
File "/usr/lib/python3.6/site-packages/sqlalchemy/orm/dynamic.py", line 278, in _clone
orm_util.instance_str(instance), self.attr.key))
sqlalchemy.orm.exc.DetachedInstanceError: Parent instance <User at 0x7fe2ac0e6e80> is not bound to a Session, and no contextual session is established; lazy load operation of attribute 'followed' cannot proceed

这是模型：

class User(db.Model):

    __tablename__ = 'user'

    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(100), unique=True)
    email = db.Column(db.String(100))
    password = db.Column(db.Binary)
    profilepic = db.Column(db.String)
    timecreated = db.Column(db.DateTime)

    #picture = db.relationship('Picture', backref='owner', lazy='dynamic')
    comment = db.relationship('Comment', backref='user', lazy='dynamic')
    post = db.relationship('Post', backref='user', lazy='dynamic')

    followed = db.relationship('Follow', foreign_keys=[Follow.follower_id],
                                backref=db.backref('follower', lazy='joined'),
                                lazy='dynamic',
                                cascade='all, delete-orphan')
    followers = db.relationship('Follow',
                                foreign_keys=[Follow.followed_id],
                                backref=db.backref('followed', lazy='joined'),
                                lazy='dynamic',
                                cascade='all, delete-orphan')

    def follow(self, user):
        if not self.is_following(user):
            f = Follow(follower=self, followed=user)
            db.session.add(f)

    def unfollow(self, user):
        f = self.followed.filter_by(followed_id=user.id).first()
        if f:
            db.session.delete(f)

    def is_following(self, user):
        return self.followed.filter_by(followed_id=user.id).first() is not None

    def is_followed_by(self, user):
        return self.followers.filter_by(follower_id=user.id).first() is not None

    @property
    def followed_posts(self):
        return Post.query.join(Follow.followed_id == Post.user_id)\
        .filter(Follow.follower_id == self.id)

    def is_authenticated(self):
        return True

    def is_active(self):
        return True

    def is_anonymous(self):
        return False

    def get_id(self):
        return str(self.id)

    def __init__(self, **kwargs):
        self.follow(self)

    def __repr__(self):
        return f'<id - {self.id} | - {self.username}>'

我想知道为什么会发生这种情况以及下次如何避免此错误

我在网上找到的唯一内容是使用lazy='subquery'而不是lazy='dynamic'，但使用它不会允许我的查询使用filter_by属性。

Answer 1

看起来您正试图通过交互式shell与您的烧瓶应用程序进行交互。您可以使用命令行界面（CLI）执行此操作。

查看文档： http://flask.pocoo.org/docs/0.12/shell/

从sqlalchemy获取错误

1 个答案: