[Python] sqlalchemy.exc.InvalidRequestError: One or more mappers failed to initialize - can't...

This error happened when I tried to get access to the page. I didn't get errors when I created the tables, but seems like there are problems still.

The models are like this:

class User(UserMixin, db.Model):
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(64), index=True, unique=True)
sell_items = db.relationship('Item', backref='user')

class Item(db.Model):
id = db.Column(db.Integer, primary_key=True)
item_name = db.Column(db.String(64), index=True)
item_image = db.Column(db.String(200), index=True)
price = db.Column(db.Float(10), index=True)
user_id = db.Column(db.Integer, db.ForeignKey('user.id'))
user = db.relationship('User', backref='sell_items')


The whole error message is this

Triggering mapper: 'Mapper|User|user'. Original exception was: Error creating backref 'user' on relationship 'User.sell_items': property of that name exists on mapper 'Mapper|Item|item'


How can I fix this? What I want to do is to refer to username who sells the item, but I cannot. There is a problem with the relationships between the models.

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