Question

I’m creating a PHP Web application, which would involve:

1) Users opening a record

2) Users making changes to the record

3) Saving changes to the record

Since this is a multi-user application, I want to prevent situations where two users have the same record open at the same time, and one user’s changes overwrites the next, preferrably by enforcing some sort of locking method when a record is opened that automatically unlocks when the user navigates away from the page.

Answer 1

By record, you mean SQL records? If so, you could add another column isOpen. Set it to 1 as long as someone else has it open, and in that case, do not serve it to anyone else.

In situations like this, it works best to also implement a timeout mechanism, where a record can be open only for ‘x’ min before being forcibly closed.

(Edit: This answer is assuming you want to keep a record locked the entire duration a user is viewing the info fetched from the table. If you want to lock a record only for the instant that a read/write operation is occuring on that record, MySQL engines have inbuilt mechanisms for that)

In response to your comment

To make a record accessible to others when the active user navigates away, off the top of my head, I can think of two ways to achieve it:

• Allow the timeout mechanism to take care of it. Depending on your scenario, a short enough time window could work fine.
• In addition to the timeout, also implement a heartbeat mechanism – an Ajax script on the page polls the server letting it know the page is still open. If the user navigates away, the server recognizes the skipped heartbeat, and unsets the record. In this case, the timeout would still take precedence. So, if the user leaves the window open and walks away, the server would still receive the heartbeat, but when the time window closes, the server unsets the record (despite still receiving heartbeats).