Cannot import name 'db' (flask, sqlalchemy)

Question

I'm trying to import database and get an error "cannot import name 'db'". I've seen answers on such problem, but none of them helped in my case. Tree of my project:

chat
  | chat.py
  └─ app
      │   models.py
      │   __init__.py
      │
      ├─── main
      │      events.py
      │      forms.py
      │      routes.py
      │      __init__.py

chat.py:

from app import create_app, socketio

app = create_app(debug=True)

if __name__ == '__main__':
    socketio.run(app)

app\init.py:

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from flask_socketio import SocketIO

socketio = SocketIO()

def create_app(debug=False):
    app = Flask(__name__)
    app.debug = debug
    app.config['SECRET_KEY'] = 'gjr39dkjn344_!67#'
    app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql:///site.db'
    db = SQLAlchemy(app)
    from .main import main as main_blueprint
    app.register_blueprint(main_blueprint)
    socketio.init_app(app)
    return app

app\main\init.py:

from flask import Blueprint

main = Blueprint('main', __name__)

from . import routes, events

app\models.py:

from app import db

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(15), nullable=False)
    session_id = db.Column(db.String(200), nullable=False)
    isready = db.Column(db.Boolean, default='False')
    room = db.relationship('Room', backref='spy')
    def __repr__(self):
        return f"User('{self.username}')"

So, when I'm trying from app import db in python terminal I get

ImportError: cannot import name 'db'

Since I'm new to flask (and web at all), I have no idea, what to do. I've tried this solution (kinda closest to my case) and all alike answers but it didn't work. What can I try?

score 1 · Answer 1 · answered Jan 15 '19 at 19:35

1

db is just a local variable in the create_app() function. You'll need to create that object outside of the create_app() factory.

You can create the Flask-SQLAlchemy db plugin object without passing in an app argument, and in the factory connect that object to te Flask app with the .init_app() method, just like you already do for the Flask-SocketIO plugin:

db = SQLAlchemy()

def create_app(debug=False):
    app = Flask(__name__)
    app.debug = debug
    app.config['SECRET_KEY'] = 'gjr39dkjn344_!67#'
    app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql:///site.db'

    db.init_app(app)
    socketio.init_app(app)

    from .main import main as main_blueprint
    app.register_blueprint(main_blueprint)

    return app

Now db is available as a global in the module, and so can be imported elsewhere.

answered Jan 15 '19 at 19:35

Martijn Pieters

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Well, I got another problem. "No application found. Either work inside a view function or push" when I try to db.create_app(). So I did it using "with app.app_context()" as it recommended in documentation, but now I can't import classes. I get "ImportError: cannot import name 'User'" – elephantsdadshusband Jan 16 '19 at 05:18
@elephantsdadshusband: those are new, independent issues. You could post those as new questions. – Martijn Pieters Jan 16 '19 at 11:37
@elephantsdadshusband: put differently: I can't solve those problems *here*, I don't have enough information nor should this question be altered to add those details. *This* specific problem has been solved, and is useful for future visitors with the same problem (which is what SO is all about). – Martijn Pieters Jan 16 '19 at 11:44

Cannot import name 'db' (flask, sqlalchemy)

1 Answers1