如何为整个龙卷风Web应用程序建立到SQLite数据库的一个连接？

Question

Now I am creating new connection to SQLite db each time I edit username. What should I do to make a single connection for a whole application?

class UserEditHandler(tornado.web.RequestHandler):
    def get(self, user_id):
        self.render('user_edit.html')

    def post(self, user_id):
        edited_name = str(self.get_arguments('name')[0])
        session = create_session()
        user_object = session.query(User).filter_by(id=user_id).first()
        user_object.name = edited_name
        session.commit()

Answer 1

There are couple solutions:

• wrap it in some singleton class (as Nikos noted)
• wrap it in separate module with global session and function get_session (effectively the same as class singleton, but in module scope)
• handle db in Application class, that is injected in RequestHandler

I would recommend third one:

import tornado 

class MyApp(tornado.web.Application):
    def __init__(self, *args, **kwargs):
        super(MyApp, self).__init__(*args, **kwargs)
        # or even initilaize connection
        self._db = None

    @property
    def db(self):
        if self._db is None:
            self._db = create_session()
        # additionally you can check here if session is time-outed or something
        return self._db


class UserEditHandler(tornado.web.RequestHandler):
    def get(self, user_id):
        self.render('user_edit.html')

    def post(self, user_id):
        edited_name = str(self.get_arguments('name')[0])
        user_object = self.application.db.query(User).filter_by(
            id=user_id
        ).first()
        user_object.name = edited_name
        self.application.db.commit()

Answer 2

One another option is to add a connection to your app settings, it will be accessible in all classes inherited form RequestHandler or WebSocketHandler.

class Application(tornado.web.Application):
    def __init__(self):
        handlers = [
            (r"/", UserEditHandler)
        ],
        settings = dict(
            db_session = create_session()
        )

class UserEditHandler(tornado.web.RequestHandler):
    def get(self, user_id):
        self.render('user_edit.html')

    def post(self, user_id):
        edited_name = str(self.get_arguments('name')[0])
        session = self.settings['db_session']
        user_object = session.query(User).filter_by(id=user_id).first()
        user_object.name = edited_name
        session.commit()

if __name__ == "__main__":
    app = Application()
    app.listen(8888)
    tornado.ioloop.IOLoop.current().start()

Also make sure to check out tornado demos for more insights https://github.com/tornadoweb/tornado/tree/master/demos