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Re: plperl no longer provides string representations of composite values

From: Mischa POSLAWSKY <postgres(at)shiar(dot)org>
To: Alex Hunsaker <badalex(at)gmail(dot)com>
Cc: pgsql-bugs(at)postgresql(dot)org
Subject: Re: plperl no longer provides string representations of composite values
Date: 2011-10-31 02:10:10
Message-ID: 20111031021010.GC4880@pearl.mediadesign.nl (view raw or flat)
Thread:
Lists: pgsql-bugs
Alex Hunsaker skribis 2011-10-28 22:03 (-0600):

> On Fri, Oct 28, 2011 at 16:42, Mischa POSLAWSKY <postgres(at)shiar(dot)org> wrote:
> > Composite types are converted to and from Perl hashes since commit
> > REL9_1_ALPHA4~146 (Convert Postgres arrays to Perl arrays on PL/perl input
> > arguments; 2011-02-17), but are not stringified as claimed by the commit
> > message and release notes (unless nested in an array).
> >
> > To illustrate:
> >
> > CREATE TYPE foo AS (bar INTEGER, baz TEXT);
> > DO $$ my $val = spi_exec_query(q< SELECT        ROW(42,'test')::foo   AS col >)->{rows}->[0]->{col}; elog(NOTICE, "$val ".ref($val)) $$ LANGUAGE plperl;
> > NOTICE:  HASH(0xb864a744) HASH
> 
> I take it this is your complaint.
> 
> > DO $$ my $val = spi_exec_query(q< SELECT ARRAY[ ROW(42,'test')::foo ] AS col >)->{rows}->[0]->{col}; elog(NOTICE, "$val ".ref($val)) $$ LANGUAGE plperl;
> > NOTICE:  {"(42,test)"} PostgreSQL::InServer::ARRAY
> 
> And you are saying this is OK.

Exactly.

> You'll note the release notes and commit message only mention that
> arrays have the backwards compatible mode. We didn't make a backwards
> compatible string version for composites as you could already pass
> those in prior to 9.1 (so really nothing changed). What did change is
> we unified most of the code so the fact that spi could return arrays
> also meant it could return hashes.

Isn't that a more important reason to provide compatibility objects though?
Regardless of accepted output, the changed input breaks all code written to
parse and/or modify a string value.

> So yes that seems like a bit of an oversight. We could fix it by doing
> something similar to what we did for arrays. That is turn composites
> from hashrefs to blessed objects and overload their string operator.
> I'm a bit worried that cure would be worse than whats "broken". Any
> code that was using ref to test for 'HASH' would now break. Arrays did
> not really have this concern because they were always a string prior
> to 9.1. Composites on the other hand have been around a lot longer--

I'm curious about where except for voluntary return values; in all of my
usage I've always received string representations upto 9.0.

> and while I know I don't have any checks like that in /my/ plperl
> code, I don't think its too far fetched to imagine someone else does.
> I suppose this is a long winded way of saying i'm not very inclined to
> dump time into "fixing" this unless there is some kind of consensus
> that we should.
> 
> Anyway I see 2 work arounds:
> - You could change your query to return text:
> SELECT        ROW(42,'test')::foo::text

Don't have a choice for function/trigger parameters.

> - use the new encode_typed_literal() function 9.1 provides

This helps, but seems to be unusable in cases where the exact composite type
is unknown.

> > # DO $$ my $q = spi_prepare('SELECT $1 AS col', 'foo'  ); elog(NOTICE, spi_exec_prepared($q,  { bar=>42, baz=>'test' } )->{rows}->[0]->{col}) $$ LANGUAGE plperl;
> > ERROR:  spi_exec_prepared: expected 1 argument(s), 0 passed at line 1.
> 
> Not really, the error here is you can't call spi_exec_prepared() like that try:
> spi_exec_prepared($q, {}, {bar=>42,...});
> 
> Per the documentation the prototype is:
> spi_exec_prepared(plan [, attributes], arguments)

I see; sorry, that's fine then.

-- 
Mischa

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