使用flask-alchemy 过程中报错KeyError: 'SQLALCHEMY_TRACK_MODIFICATIONS'

今天做一个简单的flask_sqlalchemy demo，最后在执行的时候遇到了KeyError: 'SQLALCHEMY_TRACK_MODIFICATIONS'。。。真的是不知道怎么做了，我在数据库操作页model.py页，声明了这些东西，还是报这个错

#model.py
from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.secret_key = 'development key'
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql://root:123456@localhost/test1'

#这两个值都设置了，，。。。
app.config['SQLALCHEMY_COMMIT_ON_TEARDOWN'] = True
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False

db = SQLAlchemy(app)


class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(32), unique=True)
    password = db.Column(db.String(32))\


    def __init__(self, username, password):
        self.username = username
        self.password = password

    def add(self):
        try:
            db.session.add(self)
            db.session.commit()
            return '注入数据库成功'
        except Exception as e:
            db.session.rollback()
            return e
        finally:
            return 0

    def isExisted(self):
        tempuser = User.query.filter_by(username=self.username, password=self.password).first()
        if tempuser is None:
            return 0
        else:
            return 1

后来发现大佬写的文章
https://www.cnblogs.com/zhangchenglzhao/p/9774004.html
我仔细看了下，和我的问题相似。解决方法就是只生成一个app，使用的时候引入过来就好了

# app.py
from flask import Flask, render_template, request, redirect
# 用一般的方法查询注册
# from db import *
# 用对象的方法注册查询
from model import *
from wtforms import StringField, PasswordField, validators, Form

#就是因为这两句，在这个app.py中也生成了一个app。但是没有任何设置，所以导致除了一系列的问题...
#app = Flask(__name__)
#app.secret_key = 'development key'

class loginForm(Form):
    username = StringField("username", [validators.DataRequired()])
    password = PasswordField("password", [validators.DataRequired()])


@app.route('/register', methods=["POST", "GET"])
def register():
    myForm = loginForm(request.form)
    if request.method == "POST":
        u = User(myForm.username.data, myForm.password.data)
        u.add()
        return "注册成功"
    return render_template('index.html', form=myForm)


@app.route('/login', methods=["POST", "GET"])
def login():
    myform = loginForm(request.form)
    if request.method == "POST":
        username = myform.username.data
        password = myform.password.data
        aaa = myform.validate()
        u = User(username, password)
        if u.isExisted() and myform.validate():
            return redirect('http://www.baidu.com')
        else:
            message = 'login failed'
            return render_template('index.html', message=message, form=myform)

    return render_template('index.html', form=myform)


if __name__ == '__main__':
    app.run(debug=True)