Record locking in databases with Ajax
David Perelman-Hall presents a client-based technique for record locking of multiuser data-driven web applications--and it all hinges on AJAX.
Consider this scenario: Client A calls up Record100 of a multiuser web application and begins editing it. Client B calls up the same Record100 moments later, and while Client B is modifying it, Client A saves changes to Record100. Now Client B is unwittingly modifying a record that is no longer current, and when Client B saves the record, the changes made by Client A are lost. This is an untenable situation where the last one to the finish line wins, and all others are obliterated. It would be best to find a way to inform Client B that editing is not possible as long as Client A is editing. And when Client A is done editing, it would be best to refresh Client B's view of Record100 so it includes the changes made by Client A.