flask-sqlalchemy 工程化的问题？

官方文档里的例子是直接在 app.py 里初始化数据库的，然后去用 db 但实际项目肯定不会这么做，要放文件夹里然后引入的，但我引入后就报错了

nexpect System Error - The setup method 'shell_context_processor' can no longer be called on the application. It has already handled its first request, any changes will not be applied consistently.\nMake sure all imports, decorators, functions, etc. needed to set up the application are done before running it.

• a.py

from flask import current_app
from flask_sqlalchemy import SQLAlchemy

DB = SQLAlchemy()
setting = current_app.config["Database"]
current_app.config["SQLALCHEMY_DATABASE_URI"] = f'mysql+pymysql://{setting["DB_USER"]}:{setting["DB_PASS"]}@{setting["DB_HOST"]}/{setting["DB_NAME"]}'

DB.init_app(current_app)

• b.py

from model.user import User
from a import DB

class Account:


    @staticmethod
    def login(username, password):
        user = DB.session.execute(DB.select(User).filter_by(name=username)).scalar_one()

        return "token"