Enforce FK constraint for SQLite with when using flask-sqlalchemy

flask-sqlite.py

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

def create_app(config: str=None):
    app = Flask(__name__, instance_relative_config=True)
    if config is None:
        app.config.from_pyfile('dev.py')
    else:
        logger.debug('Using %s as configuration', config)
        app.config.from_pyfile(config)

    db.init_app(app)

    # Ensure FOREIGN KEY for sqlite3
    if 'sqlite' in app.config['SQLALCHEMY_DATABASE_URI']:
        def _fk_pragma_on_connect(dbapi_con, con_record):  # noqa
            dbapi_con.execute('pragma foreign_keys=ON')

        with app.app_context():
            from sqlalchemy import event
            event.listen(db.engine, 'connect', _fk_pragma_on_connect)