Date: Mon, 11 Sep 2006 09:44:34 -0600
From: Michael Fuhr <mike@fuhr.org>
To: James Cloos <cloos@jhcloos.com>
Cc: pgsql-docs@postgresql.org
Subject: Re: plperl and triggers
Message-ID: <20060911154434.GA306@winnie.fuhr.org>
References: <m3slizm5me.fsf@lugabout.jhcloos.org>
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On Sun, Sep 10, 2006 at 11:41:38PM -0400, James Cloos wrote:
> The manual says that $_TD->{old} contains the old value of the row
> being operated on in a trigger, and $_TD->{new} the new value to be
> used istead.
> 
> When using plpgsql I find that the equivs OLD and NEW do work that
> way, but with plperlu there was only $_TD->{new}.

Are you sure the tests were identical other than the trigger function
language?  Based on your description I'd guess that you did an UPDATE
with PL/pgSQL and an INSERT with PL/PerlU.

> Perhaps {old} is only set on an update.  Or on an AFTER trigger to
> an insert?
> 
> Or perhaps {old} only gets set if {new} is altered?

New and/or old rows are available in row-level BEFORE and AFTER
triggers.  New rows are available in INSERT and UPDATE triggers;
old rows are available in UPDATE and DELETE triggers.  This behavior
should be the same in all languages; if you have an example that
shows otherwise then please post it.

> Whatever the reality, the doc should be fixed to explain exactly
> when {old} and {new} exist and their semantics.

"A patch would be welcome" :-)  The PL/Perl documentation doesn't
describe the semantics but the "Triggers" chapter does.  If you've
found a discrepancy between documentation and behavior then please
post a self-contained test case.

-- 
Michael Fuhr