Form Validation on Complex Primary Key

Question

I have a that inserts/updates a table with a 2 coulmn primary key (ticket_num, ticket_seq). Is there anyway to create a page validation item that will keep users from violating the pk constraint and getting the ugly ORA-00001 error.
I think I just don't understand the syntax of the "SQL Expression" validation.
I would like to just find if the key already exists, but the following does not seem to catch it. I have put the following in validation expression 1.
(select count(*)
from system_issue_timings
where ticket_num = :P3_TICKET_NUM
and ticket_seq = :P3_TICKET_SEQ) > 0

Answer 1

The pl/sql with count(*) above will not work as select count(*) into... will never raise no_data_found, it will result in zero in v_test.
The other thing to watch out for on this type of validation (whether implemented as sql not exists or as a pl/sql returning boolean or pl/sql returning error) is that if you are doing updates on this page then you need to either :
1. not fire the validation when updating (assuming you cannot modify the primary key columns on the page), or
2. specifically exclude the row being updated from the validation lookup (using rowid for example) as otherwise it will satisfy the condition and fail the validation.
You want to probably use 'sql NOTexists' validation as it "Passes if the query return no rows." :
select 1
from system_issue_timings
where ticket_num = :P3_TICKET_NUM
and ticket_seq = :P3_TICKET_SEQ
Glen
Edited by: gjmorris on Sep 24, 2008 1:02 PM - added actual solution.