Share sqlalchemy models between flask and other apps

The Flask-SQLAlchemy extension, like most Flask extensions, should be created outside the factory, then initialized in the factory using init_app. This is so that you can use the db object before an app is created.

db = SQLAlchemy()

def create_app():
    app = Flask(__name__)
    db.init_app(app)
    return app

Your Flask app, like any properly designed Python project, should be an installable package. This is simple to do: make sure your project layout makes sense, then add a basic setup.py file.

project/
    my_flask_package/
        __init__.py  # at the most basic, this contains create_app and db
    setup.py

from setuptools import setup, find_packages

setup(
    name="my_flask_package",
    version='1.0',
    packages=find_packages(),
    install_requires=['flask', 'flask-sqlalchemy'],
)

$ python setup.py sdist

Now you can install your Flask app, along with it’s database, for use in other projects. Install and import it in your second project’s virtualenv, then create and push an app to initialize it.

$ pip install my_flask_package-1.0.tar.gz

from my_flask_package import db, create_app
create_app().app_context().push()
db.session.query(...)

If you’re concerned about overhead involved in creating your application, you could add arguments to the create_app function to control what gets initialized. For most cases this shouldn’t be an issue though.