今日のDBIC

perl 
my $rs = $schema->resultset('Order')->search(
    {},
    {   select => [
            { date_trunc => [ 'day', 'created_on' ] }
            { count      => 'id' }
        ],
        as       => [qw/created_day order_count/],
        group_by => 'created_day',
        order_by => 'created_day',
    }
);

で動くかと思いきや動かないので

my $rs = $schema->resultset('Order')->search(
    {},
    {   select => [
            \"date_trunc ('day', created_on) as created_day",
            { count      => 'id' }
        ],
        as       => [qw/created_day order_count/],
        group_by => 'created_day',
        order_by => 'created_day',
    }
);

とした。
むーん。気持ち悪い。