Eloquent example

gistfile1.php

// http://help.laravel.io/057572a2437e89584b95082c178617e8d5fd934b

$ticketResult = $this->getInvoiceTickets()->with( array(
   'getTicket' => function ($query) {
      $query->sum('costs')->as('costs); // check the sum method in the Eloquent Builder source file
   }
  ))->get()->first();
  
  echo $ticketResult->getTicket; // or whatever the design pattern is