flask-sqlalchemy报错：The current Flask app is not registered with this 'SQLAlchemy' instance

Steak Overcooked
,
1

新手求助：
在视图文件中创建db.model类，运行正常
把模型分离出来，报错：
RuntimeError: The current Flask app is not registered with this ‘SQLAlchemy’ instance. Did you forget to call ‘init_app’, or did you create multiple ‘SQLAlchemy’ instances?

正常运行的代码如下：
【app.py】

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = r"mysql+pymysql://username:password@127.0.0.1:3306/mydb"
db = SQLAlchemy(app)

from datetime import datetime

class Category(db.Model):
    __tablename__ = "category"
    id = db.Column(db.Integer, primary_key=True, autoincrement=True, comment="自增主键ID")
    name = db.Column(db.String(20), default=None, nullable=False, comment="类别名称")

    def __init__(self, items):
        Super().__init__()
        for key in items:
            if hasattr(self, key):
                setattr(self, key, items[key])

    def __repr__(self):
        return r"类别ID:{id} 名称:{name}".format(
            id=self.id,
            name=self.name
        )

@app.route('/hello', methods=['get', 'post'])
def home():
    obj = Category.query.first()
    return str(obj)

if __name__ == '__main__':
    app.run(host="127.0.0.1", port="8008", debug=True)

报错的、分成2个文件的代码如下：
【文件1：app.py】

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = r"mysql+pymysql://username:password@127.0.0.1:3306/mydb"
db = SQLAlchemy(app)

@app.route('/hello', methods=['get', 'post'])
def home():
    from model import Category
    obj = Category.query.first()
    return str(obj)

if __name__ == '__main__':
    app.run(host="127.0.0.1", port="8008", debug=True)

【文件2：model.py】

from datetime import datetime
from app import db

class Category(db.Model):
    __tablename__ = "category"
    id = db.Column(db.Integer, primary_key=True, autoincrement=True, comment="自增主键ID")
    name = db.Column(db.String(20), default=None, nullable=False, comment="类别名称")

    def __init__(self, items):
        Super().__init__()
        for key in items:
            if hasattr(self, key):
                setattr(self, key, items[key])

    def __repr__(self):
        return r"类别ID:{id} 名称:{name}".format(
            id=self.id,
            name=self.name
        )

被这个问题堵了几个小时，网上也没查出啥，求助，万分感激！

2

在本地运行了你的程序，没有报错。

麻烦提供完整的报错输出，以及相关依赖包的版本。

3

您好，我也出现了一样的问题，请问您是怎么解决的呀？

4

报错的两个文件有互相引用，会不会出现循环引用的问题了

6 
# app.py
from flask import Flask
from model import Category, db

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = r"mysql+pymysql://username:password@localhost:3306/test"
db.init_app(app)

@app.route('/hello', methods=['get', 'post'])
def home():
    obj = Category.query.first()
    return str(obj)

if __name__ == '__main__':
    app.run(host="127.0.0.1", port="8008", debug=True)


# model.py
from flask_sqlalchemy import SQLAlchemy


db = SQLAlchemy()
class Category(db.Model):
    __tablename__ = "category"
    id = db.Column(db.Integer, primary_key=True, autoincrement=True, comment="自增主键ID")
    name = db.Column(db.String(20), default=None, nullable=False, comment="类别名称")

    def __init__(self, items):
        super().__init__()
        for key in items:
            if hasattr(self, key):
                setattr(self, key, items[key])

    def __repr__(self):
        return r"类别ID:{id} 名称:{name}".format(
            id=self.id,
            name=self.name
        )