public function getAccompanyingPeriodsOrdered() {
        $periods = $this->getAccompanyingPeriods()->toArray();
        
        //order by date :
        usort($periods, function($a, $b) {
            $dateA = $a->getOpeningDate();
            $dateB = $b->getOpeningDate();
            
            if ($dateA == $dateB) {
                $dateEA = $a->getClosingDate();
                $dateEB = $b->getClosingDate();
                
                if ($dateEA == $dateEB) {
                    return 0;
                }
                
                if ($dateEA < $dateEB) {
                    return -1;
                } else {
                    return +1;
                }
            }
            
            if ($dateA < $dateB) {
                return -1 ;
            } else {
                return 1;
            }
        });    
                
        return $periods;
    }