public function invoke($filter)
 {
     $AllDoctors = new DoctorView();
     if ($filter == "") {
         if (isset($_SESSION['role']) && $_SESSION['role'] == "Administrator") {
             $AllDoctors->showDoctors();
         } else {
             $AllDoctors->showDoctorsONLY();
         }
     } else {
         if (isset($_SESSION['role']) && $_SESSION['role'] == "Administrator") {
             $AllDoctors->showDoctorsfiltered($filter);
         } else {
             $AllDoctors->showDoctorsfilteredONLY($filter);
         }
     }
 }