Disable Trigger for a particular DELETE Query - sql

Question

I have a ruby app. The app is doing the insert,update and delete on a particular table.
It does 2 kinds of INSERT, one insert should insert a record in the table and also into trigger_logs table. Another insert is just to insert the record into the table and do nothing. Another way to put it is, one kind of insert should log that the 'insert' happened into another table and another kind of insert should just be a normal insert. Similarly, there are 2 kinds of UPDATE and DELETE also.
I have achieved the 2 types of INSERT and UPDATE using a trigger_disable. Please refer to the trigger code below.
So, when I do a INSERT, I will set the trigger_disable boolean to true if I don't want to log the trigger. Similarly I am doing for an UPDATE too.
But I am not able to differentiate between the 2 kinds of DELETE as I do for an INSERT or UPDATE. The DELETE action is logged for both kinds of DELETE.
NOTE: I am logging all the changes that are made under a certain condition, which will be determined by the ruby app. If the condition is not satisfied, I just need to do a normal INSERT, UPDATE or DELETE accordingly.
CREATE OR REPLACE FUNCTION notify_#{#table_name}()
RETURNS TRIGGER
LANGUAGE plpgsql
AS $$
DECLARE
changed_row_id varchar(100);
BEGIN
IF TG_OP = 'DELETE' THEN
-- When the trigger is due to a delete
IF (OLD.trigger_disable IS NULL)
OR (OLD.trigger_disable = false) THEN
-- Prevent the trigger if trigger_disable is 'true'
-- The Problem is here: This insertion into the
-- trigger_logs table happens
-- for all the delete statements.
-- But during certain deletes I should not
-- insert into trigger_logs
INSERT INTO trigger_logs (table_name, action, row_id, dirty)
VALUES (
'#{#table_name}',
CAST(TG_OP AS Text),
OLD.id,
true
) RETURNING id into changed_row_id;
END IF;
RETURN OLD;
ELSE
-- The trigger is due to a Insert or Update
IF (NEW.trigger_disable IS NULL)
OR (NEW.trigger_disable = false) THEN
-- Prevent the trigger if trigger_disable is 'true'
INSERT INTO trigger_logs (table_name, action, row_id, dirty)
VALUES (
'#{#table_name}',
CAST(TG_OP AS Text),
NEW.id,
true
) RETURNING id into changed_row_id;
ELSE
NEW.trigger_disable := false;
END IF;
RETURN NEW;
END IF;
END

Answer 1

I'm going to take a stab in the dark here and guess that you're trying to contextually control whether triggers get fired.
If so, perhaps you can use a session variable?
BEGIN;
SET LOCAL myapp.fire_trigger = 'false';
DELETE FROM ...;
COMMIT;
and in your trigger, test it:
IF current_setting('myapp.fire_trigger') = 'true' THEN
Note, however, that if the setting is missing from a session you won't get NULL, you'll get an error:
regress=> SELECT current_setting('myapp.xx');
ERROR: unrecognized configuration parameter "myapp.xx"
so you'll want to:
ALTER DATABASE mydb SET myapp.fire_trigger = 'true';
Also note that the parameter is text not boolean.
Finally, there's no security on session variables. So it's not useful for security audit, since anybody can come along and just SET myapp.fire_trigger = 'false'.
(If this doesn't meet your needs, you might want to re-think whether you should be doing this with triggers at all, rather than at the application level).