Problem determining if id is present in BEFORE INSERT trigger

Question

Hi,
I have written a BEFORE INSERT trigger in which I am trying to determine whether or not an id (primary key ) has been submitted as part of the insert. The reason for this is that in my application there are two cases in which the trigger will be called, 1) when the id has been previously obtained from a sequence and passed in, and 2) when an id needs to be 'automatically' generated from within the trigger'. (two subsystems which work differently talk to the database in different ways)
this is the key part of the trigger code:
CREATE OR REPLACE TRIGGER trg_submissions_seq_id
BEFORE INSERT on submissions
FOR EACH ROW
BEGIN
if :new.id IS NULL THEN
select seq_submissions_id.nextval INTO :new.id FROM DUAL;
end if;
....more code here
END;
I think this is correct. Can someone confirm this.
However the behaviour I see is that in case 1 the id is increased twice , once when it is obtained from the sequence , and then again in the trigger... despite the condition I put in.
If anyone can shed any light on this behaviour I would be grateful.
Mark

Answer 1

This trigger (at least what you've posted of it) won't increment the sequence if Rails passes in the ID column. If you're always seeing the sequence incremented twice, I would tend to wager that either Rails is calling the nextval function twice or that it is not passing in an ID. Of course, since Oracle sequence-generated values are not gap-free, presumably this is just a cosmetic issue, not a functionality issue.
As a general matter, I'd suggest not using ID as a column name for a table. In addition to being a poor naming convention, ID is a reserved word.
Justin