python - 在Flask框架中同时使用蓝图与Flask_SQLAlchemy

Question

在Flask框架中同时使用蓝图与Flask_SQLAlchemy遇到了循环导入的问题。

目录结构如下：

.
├── jade_ims
│   ├── __init__.py
│   ├── models.py
│   └── views
│       ├── home.py
│       ├── __init__.py
│       └── install.py
└── run.py

跟代码无关的部分均已去除，run.py只是单纯调用app.run()

jade_ims目录下的__init__.py文件的导入部分如下：

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from jade_ims.views.home import home
from jade_ims.views.install import install

models.py的导入部分如下：

from jade_ims import db

views目录下的install.py导入部分如下：

from flask import Blueprint, render_template, g
from jade_ims.models import User

报错提示如下：

Traceback (most recent call last):
  File "/mnt/Data/Code/jade-ims/run.py", line 1, in <module>
    from jade_ims import app
  File "/mnt/Data/Code/jade-ims/jade_ims/__init__.py", line 9, in <module>
    from jade_ims.views.install import install
  File "/mnt/Data/Code/jade-ims/jade_ims/views/install.py", line 2, in <module>
    from jade_ims.models import User
  File "/mnt/Data/Code/jade-ims/jade_ims/models.py", line 1, in <module>
    from jade_ims import db
ImportError: cannot import name 'db'

我的需求时想要在视图中直接操作db进行select，insert等操作。

全部源码可以在这里找到： https://github.com/Xuanwo/jade-ims

请问是我什么地方搞错了吗？谢谢大家。

Answer 1

I just learned flask, just tell me.

install.py

from jade_ims import app 

What the hell? Probably the first mistake

models.py

from jade_ims import db 

It should be the second mistake. The db instantiation should be placed here. If you put init, init must first register the view blueprint. The view needs to import the db class again. It is a loop. Change it to

from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy()

__init__.py
You should use factory functions. A lump of instantiation is too ugly

from flask import Flask
from werkzeug.utils import import_string
from config import config
from models import db

bps = ['jade_ims.views.home:home',
       'jade_ims.views.install:install'
        ]
        
def create_app():
    app = Flask(__name__)
    app.config.from_object('config')
    db.init_app(app)
    
    for path in bps:
        bp = import_string(path)
        app.register_blueprint(bp)
        
    return app