Migrating to Flask-SQLAlchemy 3.0

Change is the only thing that doesn't change. It's true even for software systems.
Flask-SQLAlchemy is a library that extends SQLAlchemy ORM functionalities to Flask apps. This library comes in handy for people from the Django world, which comes with its fancy ORM.
Recently they released 3.0, but there is not much information about the migration of 2.x versions to 3.x versions. I noticed the changes when I was teaching PythonToProject Bootcamp and was lost.
This post is a WIP. Please bear with me until I publish this.