my $crs = MyDBClass->resultset("Customer");

my $rs = $crs->search( undef, {
          "+select" => [
           $crs->search( { "you.id" => { '=' => \'me.id' }}, { join => { "boxes" => "devices" }, "+select" => ["devices.id"], +as =>["device_id"], alias => 'you'})->count_rs->as_query,
                       ],
          "+as" => [
                       "device_count" ,
                    ],
                                                      } );