Arbitrary SQL support in DBIx::Class need little trick to work out.
The Document is out of date.
Below is a worked example;

#!/usr/bin/perl
use strict;
use warnings;

package MySchema::ArbitrarySQL;
use base qw/DBIx::Class::Core/;

__PACKAGE__->table('dummy');
__PACKAGE__->add_columns(qw/num/);
__PACKAGE__->result_source_instance->name(\'(select 10*10 as num)');

package MySchema::LaterSQL;
use base qw/DBIx::Class::Core/;

__PACKAGE__->table('dummy');
__PACKAGE__->add_columns(qw/num/);

package MySchema;
use base qw/DBIx::Class::Schema/;

__PACKAGE__->register_class(ArbitrarySQL => 'MySchema::ArbitrarySQL');
__PACKAGE__->register_class(LaterSQL => 'MySchema::LaterSQL');


package main;

my $schema = MySchema->connect(
 "$yourdsn",  "$youruser", "$yourpass", {'RaiseError' => 1}
);
$schema->storage->debug(1);

my ($r) = $schema->resultset('ArbitrarySQL')->all;
print $r->num, "\n";

#your can even change the sql later
print $schema->source( 'LaterSQL' )->name("(select 100*100 as num)");
print "\n";

($r) = $schema->resultset('LaterSQL')->all;
print $r->num, "\n";

#but after one call, you can not change the sql
print $schema->source('LaterSQL')->name("(select 1000*1000 as num)");
print "\n";

($r) = $schema->resultset('LaterSQL')->all;
print $r->num, "\n";  #you still got 10000, that's bad.
[download]