Flask-SQLAlchemy can't find tables after upgrading from 2.5 to 3.x

Question

I'm upgrading the required packages for my Flask app and have run into a problem. I bumped up from Flask 1.1 to 2.2 and am now trying to bump Flask-SQLAlchemy up from 2.5 to 3.x. I upgraded with pip and the app starts, but when I request a page, SQLAlchemy complains that it can't find any of my tables.

I'm using SQLite locally and I can see the tables using the SQLite command line tool, so I know they exist / didn't get clobbered somehow. I assume this is just a communication issue.

Heptameter

Answer 1

Since the tables still exist, I started looking in the Flask-SQLAlchemy 3.0.0 change log, and I found this:

Configuring SQLite with a relative path is relative to app.instance_path instead of app.root_path. The instance folder is created if necessary.

My old db existed in ./my_flask_app/site.db and my config was set as "SQLALCHEMY_DATABASE_URI": "sqlite:///site.db". Flask-SQLAlchemy is now looking for it in ./instance/site.db. It had even helpfully created an empty site.db file there for me. I deleted the auto-generated one and moved the proper file into that home and everything works again.

Turns out reading the change log is helpful. Who would've thought.

Heptameter

If you do this, don't forget to exclude the instance folder from your version control, as recommended by the Flask docs: "The instance folder is designed to not be under version control and be deployment specific. It’s the perfect place to drop things that either change at runtime or configuration files." – Heptameter