Oracle Forms UNIQUE ID generation

Question

I am creating an Oracle Form. This form has a field by the name FILE_NUM. There is one more field by the name CLIENT_ID in the form. I have to generate unique FILE_NUM. The process is:

If the CLIENT_ID already exists in the table, get the FILE_NUM and assign it to the new record
ELSE, take the maximum of FILE_NUM, add 1 and assign it to the new record.

This should be taken care when multiple users are working on the form. Hence I did the following:

In Key-Commit trigger, I check if there is a lock on the table. 
If the table is locked, I make form wait for 3 second and check again.
If the table is not locked, I am locking the table and inserting the records with the above check.

My query is: is this the right way to do? Is there any other way to generate the FILE_NUM (maybe via trigger?). The problem with key-commit trigger is that if the form closes forcefully, the lock is not removed. This will cause more issues, hence I want to remove the lock feature.

Please advice.

Answer 1

This is the correct way, but indeed the lock can stay in some cases. If the number doesn't have to follow each other you can use a sequence instead. This will give you a number when needed and it will be unique.