Constraint in Trigger

Question

I had written a trigger as given below. But somehow its not checking the condition i had set in the trigger.
IF Q1 > Q2 THEN RAISE BAD;
Trigger
CREATE OR REPLACE TRIGGER "CM_RECIPE_ITEM_T3"
BEFORE INSERT OR UPDATE
ON "CM_RECIPE_ITEM"
FOR EACH ROW
DECLARE
Q1 NUMBER;
Q2 NUMBER;
BAD EXCEPTION;
BEGIN
SELECT SUM(CRI_QTY)
INTO Q1
FROM CM_RECIPE_ITEM
WHERE CRI_CR_ID = :NEW.CRI_CR_ID;
SELECT CR_QUANTITY
INTO Q2
FROM CM_RECIPE
WHERE CR_ID = :NEW.CRI_CR_ID;
IF INSERTING OR UPDATING
THEN
IF Q1 > Q2
THEN
RAISE BAD;
END IF;
END IF;
EXCEPTION
WHEN BAD
THEN
raise_application_error (-103, 'CRI_QTY exceeding the BOM Qty');
END;
Yogesh

Answer 1

Hi Yogesh,
I think you're logic may be wrong. I assume what you are trying to do is check that the sum of CRI_QTY in the child table does not exceed the maximum CR_QUANTITY as specified in the parent table for a given CR_ID.
I think where you are going wrong is that the trigger is doing the test before the insert or update on the recipe_item so that the trigger never sees the new or changed value. It may see it subsequently where it may then throw up the error, but this will be too late. You should either do the test after insert or update (may cause mutating problems) or you should allow for the new or updated value in the trigger logic.
You should also note that you may run into multi-user concurrency problems with this logic as two users may independently be able to pass the test but collectively may invalidate the logic.
Regards
Andre