To: Jeff Post <POSTJL@milwaukee.k12.wi.us>
Cc: pgsql-sql@postgresql.org
Subject: Re: Preventing Deletions with triggers 
In-reply-to: <6.1.0.6.0.20040519090934.025963a8@mail.milwaukee.k12.wi.us> 
References: <6.1.0.6.0.20040519090934.025963a8@mail.milwaukee.k12.wi.us>
Comments: In-reply-to Jeff Post <POSTJL@milwaukee.k12.wi.us>
	message dated "Wed, 19 May 2004 09:19:47 -0500"
Date: Fri, 21 May 2004 11:28:52 -0400
Message-ID: <4042.1085153332@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Jeff Post <POSTJL@milwaukee.k12.wi.us> writes:
> CREATE or replace FUNCTION person_fake_delete() RETURNS TRIGGER AS '
>      BEGIN
>          OLD.status := 1; -- This does the fake deletion
>          RETURN NULL;  -- I thought this would prevent the delete from 
> actually happening.
>      END;
> ' LANGUAGE 'plpgsql';

> create trigger person_fake_delete
> before delete on person
> for each row EXECUTE PROCEDURE
> person_fake_delete();

> This however does not work.  the tupple is still deleted from the 
> table.    Any Ideas?

It works for me, in the sense that returning NULL prevents the
deletion.  However that assignment to OLD is a no-op: you can't change
the tuple that way.  You'd have to do something like

	UPDATE person SET status = 1 WHERE key = OLD.key;

("key" being whatever your primary key for the table is)

			regards, tom lane