Notification handling in a postgresql database

Question

Im designing a database for a web app.

I'm struggling with the notifications topic: in my web app there will be a forum with messages, comments, and users. I would like users to be notified when someone answer their post and when comments are added to their posts, or when they follow a post.

I dont understand if I need to :

a) code a listener in my django (python) backend to monitor the database and populate the notification table in the database, or code each database message and comment handling so it creates notifications in the database also?

b) or if I can design the database so it autopopulates a notification table I can thereafter use in my backend?

c) or if I need to code my frontend so each action of the user populates at the same time the message/comment and notification tables?

Can someone give me a hint?

edit : No answers or comments yet...should i post this on dba stackexchange forum? Thank you