flask-sqlalchemy:导入模型出错 [英] flask-sqlalchemy: import models going wrong

问题描述

我正在使用Flask和Sqlalchemy构建一个应用程序.我的 app.py 文件开始如下:

I am building an app with Flask and Sqlalchemy. My app.py file starts like this:

from flask import Flask
from flask.ext.sqlalchemy import SQLAlchemy
app = Flask(__name__)
db = SQLAlchemy(app)
from models import User

和我的 models.py 像这样:

from app import db
class User
....

因此，当我运行 python app.py 时，出现错误消息无法导入用户名".我想某处有一个循环导入，我不知道如何解决它.

so when I run python app.py, I get an error saying "cannot import name User". I guess there's a circular import somewhere, I don't understand how to fix it.

但是，如果我仅用

from app import app
app.run()

一切正常.但是，为什么这会中断循环导入?我不明白.

Everything works perfectly. But why does this break circular import? I can't understand this.

推荐答案

您做对了:这是一个循环导入问题.

You've got it right: this is a circular import problem.

解决这个问题的方法是在根目录中有另一个文件，即 shared.py 文件.在该文件中，创建数据库对象，

The way that I've gotten around this is by having another file, a shared.py file in the root directory. In that file, create the database object,

from flask.ext.sqlalchemy import SQLAlchemy
db = SQLAlchemy()

在您的 app/init.py 中，不要创建新的数据库对象.相反，

In your app/init.py, don't create a new db object. Instead, do

from shared import db
db.init_app(app)

在您想使用db对象的任何地方(包括模型文件)，从 shared.py 导入它:

In any place that you want to use the db object, including your models file, import it from shared.py:

from shared import db
# do stuff with db

这样，共享文件中的对象将已使用应用程序上下文进行了初始化，并且没有循环导入的机会.

This way, the object in the shared file will have been initialized with the app context, and there's no chance of circular imports.

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