EDIT: Ack, nevermind the example below the <hr>, I missed the PL/Perl part of the question. Inside PL/Perl, if the array values are represented by strings, then you could parse them into Perl arrays, manipulate them, and then format them back into Postgres's string form using Rose::DB's parse_array() and format_array() methods. But that's hardly efficient when compared to some sort of "native" manipulation within PL/* ... :-/

AFAIK, there's no good way to apply any fancy tricks to DBD::Pg's internals because the array values all get stringified once they actually leave the database. (i.e., By the time DBD::Pg gets them, they're strings). Last time I checked, even Postgre's native PL/PgSQL language isn't too great at manipulating array values in-place (push, pop, splice, etc.) which leads me to believe that Pg's array value internal representation is not "public." (If it was presumably PL/PgSQL, at least, would know how to manipulate it.) Maybe Pg 8.x improved this?

Asking on the pgsql-general mailing list is your best bet. They can direct you to a more specific list if no one on "general" can answer your questions.

Anyway, here's the string-based version:

use Rose::DB;

Rose::DB->register_db
(
  domain => 'default',
  type   => 'default',
  driver => 'Pg',
);

$db = Rose::DB->new;

$s = '{2,"four",6,8}';
$a = $db->parse_array($s);

pop(@$a);
$a->[2]++;

$f = $db->format_array($a); # '{2,"four",7}'

[download]

I've got a column type for Postgres's native array type in Rose::DB::Object. It's the way I manipulate Postgres's array column values on the Perl side of things:

The table:

CREATE TABLE mywidgets
(
  id    SERIAL NOT NULL PRIMARY KEY,
  name  VARCHAR(255) NOT NULL,
  nums  INT[]
);

[download]

The class:

package MyWidget;
use base 'Rose::DB::Object';

MyWidget->meta->table('mywidgets');

MyWidget->meta->columns
(
  id   => { type => 'serial', not_null => 1, primary_key => 1 },
  name => { type => 'varchar', length => 255, not_null => 1 },
  nums => { type => 'array' },
);

MyWidget->meta->error_mode('fatal');
MyWidget->meta->initialize;

1;

[download]

Examples of array column value manipulation:

$n = MyWidget->new(name => 'Sprocket',
                   nums => [ 2, 4, 6, 8 ]);
$n->save;

$n2 = MyWidget->new(id => $n->id);

$n2->load;

print $n2->nums->[1]; # 4

[download]

In reply to Re: PostgreSQL arrays -> Perl arrays by siracusa
in thread PostgreSQL arrays -> Perl arrays by davidfetter

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