Reflecting Tables, "'autoload_with': db.engine" working outside context

[TRezendes]

I know that my issue is to do with the changes related to app context in Flask 2.2.x and Flask-SQLAlchemy 3.x, and I know that I need to push a context in order to get my code to work, but I am unsure of where and exactly how to do so. Any help would be appreciated.

All of the tables in my models.py file take advantage of SQLAlchemy's ability to reflect database objects. Flask fails to run because 'autoload_with': db.engine' throws a Runtime Error.

models.py

from appname_app import argon2, db
from flask_login import UserMixin
from sqlalchemy.dialects import postgresql
from sqlalchemy import PrimaryKeyConstraint

class UserInfoTbl(db.Model):
    __tablename__ = 'user_info'
    __table_args__ = {
        'autoload':True,
        'autoload_with': db.engine
}

…

init.py

from flask import Flask, render_template, url_for, redirect, request
from flask_sqlalchemy import SQLAlchemy
from flask_wtf.csrf import CSRFProtect
from flask_login import LoginManager
from flask_argon2 import Argon2
import json

db = SQLAlchemy()
argon2 = Argon2()
csrf = CSRFProtect()
login_manager = LoginManager()

def create_app():
    app = Flask(__name__)
    
    with open('config.json') as config_file:
        config = json.load(config_file)

    # General configuration
    app.config['SECRET_KEY'] = config.get('SECRET_KEY')
    app.config['SQLALCHEMY_DATABASE_URI'] = config.get('DEV_DATABASE_URI')
    app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = config.get('SQLALCHEMY_TRACK_MODIFICATIONS')  

    db.init_app(app)
    db.app = app

…

The app works as expected with Flask==2.1.3 & Flask-SQLAlchemy==2.5.1, but with Flask==2.2.2 & Flask-SQLAlchemy==3.0.2 I get the error:

…
  File "appname_app/models.py", line 7, in <module>
    class UserInfoTbl(db.Model):
  File "appname_app/models.py", line 11, in UserInfoTbl
    'autoload_with': db.engine
  File "/Users/trezendes/.pyenv/versions/3.10.6/envs/APPNAME/lib/python3.10/site-packages/flask_sqlalchemy/extension.py", line 642, in engine
    return self.engines[None]
  File "/Users/trezendes/.pyenv/versions/3.10.6/envs/APPNAME/lib/python3.10/site-packages/flask_sqlalchemy/extension.py", line 628, in engines
    app = current_app._get_current_object()  # type: ignore[attr-defined]
  File "/Users/trezendes/.pyenv/versions/3.10.6/envs/APPNAME/lib/python3.10/site-packages/werkzeug/local.py", line 513, in _get_current_object
    raise RuntimeError(unbound_message) from None
RuntimeError: Working outside of application context.

[TRezendes]

I spent about a day trying to sort this problem out before I posted this question, but I should have given myself a couple more hours. I am going to answer my own question in case anyone else comes looking.

I was able to resolve my "outside of application context" error with the following changes (in bold italic) to my models.py:

models.py

from appname_app import argon2, db, create_app
from flask_login import UserMixin
from sqlalchemy.dialects import postgresql
from sqlalchemy import PrimaryKeyConstraint

app = create_app()
with app.app_context():        
    class UserInfoTbl(db.Model):
        __tablename__ = 'user_info'
        __table_args__ = {
            'autoload':True,
            'autoload_with': db.engine
    }