Flask, Marshmallow and Sqlalchemy factory problems

Question

I am building a Flask RESTful application and I'm trying to build it with a factory design pattern but I think I'm missing something. Here are my set up files

app.py: `

from src import create_app, ext_celery

app = create_app("development")
celery = ext_celery.celery

src/init.py:

db = SQLAlchemy()
ext_celery = FlaskCeleryExt(create_celery_app=make_celery)

def create_app(config_name=None):
    app = Flask(__name__)
    app.config.from_object(config[config_name])

    db.init_app(app)
    ext_celery.init_app(app)

    api = Api(app, errors=errors)
    initialize_routes(api)

    return app

My problem is in the user/view.py file. If I try put the db import statement at the top of the file I get a circular reference error:

ImportError: cannot import name 'db' from partially initialized module 'src' (most likely due to a circular import) (/app/src/__init__.py)

so I have to move it inside of the method in order for it to work. My user/view.py put function looks like this:

    @token_required
    def put(self, user):
        data = request.json
        from .schema import user_get_schema
        from src import db
        updated_user = user_get_schema.load(data, session=db.session)
        from models import Users
        ...

I get the same issue if I try to import the schema or the models above the method call. Is this how it's supposed to work? I have to import these items for EVERY view? That doesn't seem right to me but I can't figure out how else to do it. I'm still trying to learn Python.

Thank you

Answer 1

You are using a circular import. You should move all connection 3rd app to another file like src/extension.py

src/extension.py

from flask_sqlalchemy import SQLAlchemy
from flask_celeryext import FlaskCeleryExt


db = SQLAlchemy()
ext_celery = FlaskCeleryExt(create_celery_app=make_celery)

src/init.py:

from src.extension import db, ext_celery

def create_app(config_name=None):
    app = Flask(__name__)
    app.config.from_object(config[config_name])

    db.init_app(app)
    ext_celery.init_app(app)

    api = Api(app, errors=errors)
    initialize_routes(api)

    return app

In all file models or view you will use from src.extension import db. Now all file will import from one connection from one file to avoid circular import

Answer 2

That gets me one step closer but I have a context problem in my models class now:

class Models:
    Base = automap_base()
    from app import app
    with app.app_context():
        Base.prepare(autoload_with=db.engine)
    Users = Base.classes.users

how do I get access to the app_context() without the circular import?

update

I hate hacks like this but I also hate spending the several days turning in circles trying to figure out something that I don't understand. So I'm creating an entirely new Flask app in models in order to gain access to context...ugh

config_name = os.environ.get("FLASK_CONFIG", "development")
app = Flask(__name__)
app.config.from_object(config[config_name])
db = SQLAlchemy()
db.init_app(app)
Base = automap_base()
with app.app_context():
    Base.prepare(autoload_with=db.engine)