Thanks.

So even for queries that don't use a table you have to set a table (any dummy value will do).

Here a complete working example:

package TA::CP::DB::Schema::Result::CustomTest;

use strict;
use warnings;
use base qw/DBIx::Class::Core/;

__PACKAGE__->table_class('DBIx::Class::ResultSource::View');
__PACKAGE__->table('DUMMY');
__PACKAGE__->add_columns("x");

__PACKAGE__->result_source_instance->is_virtual(1);

__PACKAGE__->result_source_instance->view_definition("select 2*2 as x"
+);
[download]

This can then be used as usual:

my ($res) = $schema->resultset("CustomTest")->all;

print $res->x;  # prints 4
[download]

</c>