If I'm writing a ticketing system, where the customer selects the ticket and I want to lock it for 3 minutes (like ticket master) until they complete their order or time runs out, how could I do this? I want to avoid having a customer abandon their session/application crash and then end up with the ticket locked in the database forever.
I'm using nHibernate for my ORM and C#.
Just have a separate table that holds all current reservations. For example:
**Reservations**
UserID
TicketID
ExpiryDate
This will then not be dependant on sessions. You don't even need to delete expired records, when a new customer queries a ticket find all seats that are available where they dont exist in the reservations table where the expirydate > now.
Avoid more complex systems of timed events and things like that, keep it simple.
Have a ticket expiry service that periodically unlocks expired ticket locks. Record the expiry time and the ticket (possibly with a session id). The the order could remove this when no longer needed or in case of faliure it will be automatically unlocked.
If you can identify each ticket, you can assign locking information to this ticket with data about user, order, etc and of course - timestamp wich holds time when lock expires.
If another user wants to select the ticket, you just need to check this timestamp to see if the lock has expired.
