models.py

class IdModel:
    id = db.Column(db.Integer, primary_key=True)


class User(IdModel, UserMixin, db.Model):
    username = db.Column(db.String(64), index=True, unique=True)
    email = db.Column(db.String(128), index=True, unique=True)
    password_hash = db.Column(db.String(128))

    def __repr__(self):
        return '<User {}>'.format(self.username)

    def set_password(self, password):
        self.password_hash = generate_password_hash(password)

    def check_password(self, password):
        return check_password_hash(self.password_hash, password)

    @classmethod
    @login.user_loader
    def load_user(cls, id_):
        return cls.query.get(int(id_))