Question : check if record is already locked

When a user retrieves a record, I would like to be able to check if the record has been locked by someone else.  If not, I want to be able to lock it, run an update statement if needed and release the record again.  I want that check to be done when the data is retrieved, regardless of whether the user chooses to change something on the form.

Which trigger should I use and how do I go about checking whether the record can be reserved or not?

Answer : check if record is already locked

if u use an "for update NOWAIT" in  sql statement, THEN IT raise an exception saying it is locked, otherwise continue with updation.