Re: Recursion in triggers?

On 24 Jan 2010, at 5:36, Gauthier, Dave wrote:

> Hi:
>
> I’m dealing with a hierarchical design where changes in one record can and should cause changes in other records lower inthe hierarchy. I’m trying to use update triggers to do this. And recursion would be a real nice way to do this.
>
> What I need to know is if, in the “after” update trigger I make the subsequent updates to other records in the same table, with the OLD/NEW record ponters be set properly in those subsequent update trigger invocations? Will the current and modified NEW.* values be passed down into the next update trigger “before” call as OLD.* values? Or is recursion like this not allowed?

I'm not really sure what you're trying to do, so it's a tad hard to answer.

Are you using multiple before-update triggers on the SAME table? In that case you ask an interesting question that I don't know the answer to either. I do know that they'll fire ordered alphabetically on trigger name.

A test case with a few raise notices is easily created though:

BEGIN;

CREATE FUNCTION x()
RETURNS trigger
AS $$
BEGIN
RAISE NOTICE 'OLD.test = %, NEW.test = %', OLD.test, NEW.test;

NEW.test := New.test + 1;

RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TABLE trigger_test(test int);
INSERT INTO trigger_test VALUES (1);

CREATE TRIGGER a BEFORE UPDATE ON trigger_test
FOR EACH ROW EXECUTE PROCEDURE x();

CREATE TRIGGER b BEFORE UPDATE ON trigger_test
FOR EACH ROW EXECUTE PROCEDURE x();

SET client_min_messages TO notice;

UPDATE trigger_test SET test=2 WHERE test=1;

ROLLBACK;

development=> \i /tmp/trigger_test.sql
BEGIN
CREATE FUNCTION
CREATE TABLE
INSERT 0 1
CREATE TRIGGER
CREATE TRIGGER
SET
psql:/tmp/trigger_test.sql:26: NOTICE: OLD.test = 1, NEW.test = 2
psql:/tmp/trigger_test.sql:26: NOTICE: OLD.test = 1, NEW.test = 3
UPDATE 1
ROLLBACK

Alban Hertroys

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