To: "Nekta Katz" <nekta_k@hotmail.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: cast lo to oid 
In-reply-to: <F21wAeRaNgEpTX5V3Gy00000652@hotmail.com> 
References: <F21wAeRaNgEpTX5V3Gy00000652@hotmail.com>
Comments: In-reply-to "Nekta Katz" <nekta_k@hotmail.com>
	message dated "Thu, 07 Nov 2002 23:22:26 +1100"
Date: Thu, 07 Nov 2002 10:16:21 -0500
Message-ID: <19382.1036682181@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

"Nekta Katz" <nekta_k@hotmail.com> writes:
> I have the following table

> create table scan_docs (
>     docid   serial,
>     shipno numeric(10),
>     scan    lo,
>     type text
> );

> when I try to create the following rule

> create rule "delete_scan_docs_lo" as
> on delete to "scan_docs"
> do select lo_unlink (old.scan);

Why aren't you using the trigger that type LO provides for this purpose?
Seems rather pointless to use a nonstandard type and then ignore the
primary (sole) feature it provides...

> create rule "delete_scan_docs_lo" as
> on delete to "scan_docs"
> do select lo_unlink (old.scan::oid);

> "psql:scan_docs_rule.sql:3: ERROR:  Cannot cast type 'lo' to 'oid' "

Curious, as contrib/lo provides a function that's supposed to work
for that:

-- same function, named to allow it to be used as a type coercion, eg:
--    CREATE TABLE a (image lo);
--    SELECT image::oid FROM a;
--
CREATE FUNCTION oid(lo)
RETURNS oid
AS 'MODULE_PATHNAME', 'lo_oid'
LANGUAGE 'C';

What PG version are you using?

			regards, tom lane