application not registered on db instance and no application bound to current context

直接使用 db.create_all() 會出錯，改成以下

with app.app_context():
    db.create_all()

問題說明：
Flask and SQLAlchemy: init_app · Piotr Banaszkiewicz




References :
python - When scattering Flask Models, RuntimeError: 'application not registered on db' was raised - Stack Overflow