How to connect to flask-sqlalchemy database from inside a RQ job - python-3.x

Question

Using flask-sqlalchemy, how is it possible to connect to a database from within a redis task?
The database connection is created in create_app with:
db = SQLAlchemy(app)
I call a job from a route:
#app.route("/record_occurrences")
def query_library():
job = queue.enqueue(ApiQueryService(word), word)
Then inside the redis task, I want to make an update to the database
class ApiQueryService(object):
def __init__(self,word):
resp = call_api()
db.session.query(Model).filter_by(id=word.id).update({"count":resp[1]})
I can't find a way to access the db. I've tried importing it with from app import db. I tried storing it in g. I tried reinstantiating it with SQLAlchemy(app), and several other things, but none of these work. When I was using sqlite, all of this worked, and I could easily connect to the db from any module with a get_db method that simply called sqlite3.connect(). Is there some simple way to access it with SQLAlchemy that's similar to that?

Answer 1

This can be solved using the App Factory pattern, as mentioned by #vulpxn.
Let's assume we have our configuration class somewhere like this:
class Config(object):
DEBUG = False
TESTING = False
DEVELOPMENT = False
API_PAGINATION = 10
PROPAGATE_EXCEPTIONS = True # needed due to Flask-Restful not passing them up
SQLALCHEMY_TRACK_MODIFICATIONS = False # ref: https://stackoverflow.com/questions/33738467/how-do-i-know-if-i-can-disable-sqlalchemy-track-modifications/33790196#33790196
class ProductionConfig(Config):
CSRF_COOKIE_SAMESITE = 'Strict'
SESSION_PROTECTION = "strong"
SESSION_COOKIE_SECURE = True
SESSION_COOKIE_HTTPONLY = True
SESSION_COOKIE_SAMESITE = 'Strict'
SECRET_KEY = "super-secret"
INVITES_SECRET = "super-secret"
PASSWORD_RESET_SECRET = "super-secret"
PUBLIC_VALIDATION_SECRET = "super-secret"
FRONTEND_SERVER_URL = "https://127.0.0.1:4999"
SQLALCHEMY_DATABASE_URI = "sqlite:///%s" % os.path.join(os.path.abspath(os.path.dirname(__file__)), "..",
"people.db")
We create our app factory:
from flask_sqlalchemy import SQLAlchemy
from flask import Flask
from development.config import DevelopmentConfig
from rq import Queue
from email_queue.worker import conn
db = SQLAlchemy()
q = Queue(connection=conn)
def init_app(config=ProductionConfig):
# app creation
app = Flask(__name__)
app.config.from_object(config)
# plugin initialization
db.init_app(app)
with app.app_context():
# adding blueprints
from .blueprints import api
app.register_blueprint(api, url_prefix='/api/v1')
return app
We will now be able to start our app using the app factory:
app = centrifuga4.init_app()
if __name__ == "__main__":
with app.app_context():
app.run()
But we will also be able to (in our Redis job), do the following:
def my_job():
app = init_app()
with app.app_context():
return something_using_sqlalchemy()