/**
  * @param Project $project
  * @param int     $service_id
  *
  * @return Project_Service_ServiceUsage
  */
 public function getServiceUsage(Project $project, $service_id)
 {
     $query_result = $this->dao->getServiceUsage($project->getID(), $service_id);
     $row = $query_result->getRow();
     if ($row) {
         return $this->getInstanceFromRow($row);
     }
     return null;
 }