Django/SQL: keeping track of who who read what in a forum

I'm working on a not-so-big project in django开发者_如何学Go that will among other things incorporate a forum system.

I have most of the system at a more or less functioning state, but I'm still missing a feature to mark unread threads for the users when there are new posts.

The thing is I can't really think of a way to properly store that information. My first idea was to create another model that will store a list of threads with changes in them for each user. Something with one ForeignKey(User) and one ForeignKey(Thread) and just keep adding new entries each time a thread is posted or a post is added to a thread.

But then, I'm not sure how well that would scale with say several hundred threads after a while and maybe 50-200 users. So add 200 rows for each new post for the users who aren't logged on? Sounds like a lot.

How do other forum systems do it anyway? And how can I implement a system to work these things out in Django.

Thanks!

You're much better off storing the "read" bit, not the "unread" bit. And you can store them not as relational data, but in a giant bit-blob. Then you don't have to modify the read data at all when new posts are added, only when a user reads posts.

You might also simply store the last time a user was reading a particular forum. Any posts that have been updated since that date are new. You'll only be storing one additional piece of information per user as opposed to a piece of information per post per user.