public function getUniqReference()
    {
        $query = new DbQuery();
        $query->select('MIN(id_order) as min, MAX(id_order) as max');
        $query->from('orders');
        $query->where('id_cart = '.(int)$this->id_cart);
        
        $order = Db::getInstance()->getRow($query);
        
        if ($order['min'] == $order['max'])
            return $this->reference;
        else
            return $this->reference.'#'.($this->id + 1 - $order['min']);
    }

public function getUniqReference()
    {
        return '№'.$this->id;
    }

{$reference}

$reference

{$id_order}

$id_order