Perl DBIx::Class: select attribute not precluding other fields - sql

Question

I'm trying to use a DBIx::Class ResultSet to build:
SELECT commitment_sub_activity_id, SUM(commitment_amount_in_usd)
FROM query_commitments_financials
GROUP BY (commitment_sub_activity_id)
Here's the Perl code I'm trying to use to do this:
my $sub_activity_commitments = $schema->resultset('QueryCommitmentsFinancial')->search(undef,
{
select => [
'commitment_sub_activity_id',
{ sum => 'commitment_amount_in_usd' }
],
as => [qw/commitment_sub_activity_id total_commitment_in_usd/],
'group_by' => [qw/commitment_sub_activity_id/],
});
As I understand it, the select attribute should prevent any unlisted fields from appearing in the SELECT statement. However, the SQL statement DBIx::Class creates comes out as:
SELECT
me.source_id, me.commitment_id,
me.commitment_obligation_id, me.commitment_sub_activity_id,
me.commitment_task_code, me.commitment_status,
me.commitment_date, me.commitment_currency_id,
me.commitment_amount, me.exchange_rate,
me.commitment_amount_in_usd, me.commitment_sub_activity_id,
SUM( commitment_amount_in_usd )
FROM query_commitments_financials me
GROUP BY commitment_sub_activity_id
This query causes my RDBMS to throw an error because those unexpected columns would all need to be included in the GROUP BY.
What is the correct way to get the DBIx::Class ResultSet to build this aggregate query?
UPDATE: Providing the ResultClass definition of QueryCommitmentsFinancial as requested. I used DBIx::Class::Schema::Loader to create it, so I removed the POD.
use utf8;
package IPMS::Schema::Result::QueryCommitmentsFinancial;
use strict;
use warnings;
use base 'DBIx::Class::Core';
__PACKAGE__->load_components("InflateColumn::DateTime");
__PACKAGE__->table_class("DBIx::Class::ResultSource::View");
__PACKAGE__->table("query_commitments_financials");
__PACKAGE__->add_columns(
"source_id",
{ data_type => "nvarchar", is_nullable => 1, size => 52 },
"commitment_id",
{ data_type => "nvarchar", is_nullable => 1, size => 51 },
"commitment_obligation_id",
{ data_type => "nvarchar", is_nullable => 1, size => 45 },
"commitment_sub_activity_id",
{ data_type => "integer", is_nullable => 0 },
"commitment_task_code",
{ data_type => "nchar", is_nullable => 0, size => 7 },
"commitment_status",
{ data_type => "nvarchar", is_nullable => 0, size => 10 },
"commitment_date",
{ data_type => "datetime", is_nullable => 1 },
"commitment_currency_id",
{ data_type => "integer", is_nullable => 0 },
"commitment_amount",
{ data_type => "money", is_nullable => 1 },
"exchange_rate",
{ data_type => "double precision", is_nullable => 1 },
"commitment_amount_in_usd",
{ data_type => "money", is_nullable => 1 },
);
1;