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Data Locking In a Web Application?
An anonymous reader writes "We recently developed a multi-user application and deployed it to our users. This is a web-based application that used to be a Windows application which was written in Delphi using Paradox databases for the client database. In the Windows application, we used the ability in Paradox to lock records which would prevent users from editing the same data. However, in the web application we did not add in a locking facility for the data due to its disconnected nature (at least that's how I was shot down). Now our users are asking to have the locking back, as they are stepping on each others' edits from time to time. I have been assigned to look at best practices for web application locking of data, and figured I would post the question here to see what others have done or to get some pointers to locations for best practices on doing locking with in a web application. I have an idea of how to do this, but don't want to taint the responses so I'll leave it off for the time being."
My company has an internal app that approaches locking in a different manner. When you start updating a record, it uses an AJAX routine to set a lock on the record being updated. As long as you're still on that page, you "have the lock" and other users are notified of this if they attempt to edit the record. Once your changes are submitted, the lock is released automatically. It's possible to "steal" a lock in our model; this may not work for everyone. If you didn't want to allow this, you could incorporate a timeout for locks, whereby the original user would be notified that the lock had expired due to inactivity.
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When you are ordering tickets through TicketMaster.com, they hold the seat assignment for you for 10 minutes. If you don't complete the transaction within that time frame, the tickets become public again.
In your database setting, the user Alice wants to edit the customer Carol's record. The application gives Alice a lock on Carol's record for five minutes. If user Bob tries to edit Carol's record within the five minute window, he gets a message telling him to wait for 3:42 while Alice finishes her edit. When Alice is finished, the lock is released and if she doesn't finish in five minutes, the lock is released anyway and her edits are lost.
You could also add the ability for the user to set the lock time, within a reasonable window, say 5-15 minutes. Also, consider adding the ability for the user to renew the lock.
BTW - Paradox is still around? I haven't used it since 1993 or so. Wow.