How to access other module data table SugarCRM

I am writing logic hook and I need to update 1 module fields by using other module elements.

<?php
class logic_hooks_class {

function after_save_method($bean, $event, $arguments) {

    if (!isset($bean->ignore_update_c)||$bean->ignore_update_c === false {

     //here I need to get module's reservations element: amount_reserved 
     //should I load relationship like $bean->load_relationship('reservations'); ??
     //need to set total_reserved = amount_reserved;
     //by the way amount_reserved might have several values for one reserved

          $bean->goods = $bean->amount-$bean->total_reserved;
          $bean->ignore_update_c = true;
          $bean->save();
  }
 }
}
?>

You can load the beans for the relationship like this:

$bean->load_relationship('reservations');
$reservations = $bean->reservations->getBeans();

Now one can loop the $reservations and fetch and sum up the wanted value.

Just to clarify how load_relationship works. The parameter for load_relationship should be the link vardef pointing to the name of the relationship. A logical name is the plural name for the module, like reservations.