Building a notification system [closed]

Answer 1

╔════════════════════╗
║notification        ║
╟────────────────────╢
║Username            ║
║Object              ║
║verb                ║
║actor               ║
║isRead              ║
╚════════════════════╝

This looks a good answer rather than having 2 collections. You can query by username, object and isRead to get new events(like 3 pending friend requests, 4 questions asked etc...)

Let me know if there is problem with this schema.