Mutating table exception on trigger with After Insert but not with before

Question

Hi
I need to maintain some constraint on the table to have only one row for values of the columns but not by primary key constraint.
Because in case of primary key the insert would fail and the rest of the operation would be discontinued, I cannot change in the somponent that inserts the row so I have to prevent that on the table I have.
I created a before insert trigger on the table which checks if any row exists in the table with same column values as the one being inserted. if found I delete the rows and let the insert happen (w/o raising any error). if the rows do not exist then the insert shall be continued.
I read at place that modifying the dame table in the trigger body shall raise a mutating table exception, but I donot get the exception when the trigger is fired.
Just when I change the trigger to after insert trigger then the nutating table exception is thrown.
Is it the right behavior i.e. the Before insert trigger does not raise the exception and only after insert does that, since I could not find the example for before insert triggers throwing such exception so I think it is better to confirm it before finalizing the implementation.
Thanks
Sapan

Answer 1

sapan wrote:
Hi Tubby
I cannot user unique constraint because that would raise an exception upon violation and the third party component that is inserting in the table would fail.
That component does some other tasks as well after this insert and if an exception is raised then those tasks would not be performed.
Also I cannot change the component to ignore this exception.Well then, you're in a bit of a pickle.
I'm guessing the trigger you have been working on isn't "safe". By that i mean that it doesn't account for multi-user scenarios. You'll need to serialize access to the data elements in question and implement some sort of locking mechanism to ensure that only 1 session can work with those values.
After you work out how to do that it sounds as though you would be better served using an INSTEAD OF trigger (you'd need to implement this on a view which is made off of your base table).
Here's one way you can work on serializing access to your table on a relatively fine grained level (as opposed to locking the entire table).
Re: possible to lock stored procedure so only one session may run it at a time?
Cheers,