php - Limiting the number of radio buttons checked by a user after submit in Symfony2 form -

i new symfony2. have created form has 3 sets of radio buttons , submit button. display form, have used formtype. now, have apply condition user can select maximum of 2 sets of radio buttons(and minimum of 0 sets of radio buttons) , not 3 sets of radio buttons. if user selects 3 sets of radio buttons , clicks on submit want throw error message user saying "you can select 2".

this formtype "subscriptionstype.php"

 <?php   namespace instituteevents\studentbundle\form\type;  use symfony\component\form\abstracttype;  use symfony\component\form\formbuilderinterface;   class subscriptionstype extends abstracttype { public function buildform(formbuilderinterface $builder, array $options) {  $builder  ->add('event1', 'choice', array('choices' => array('1' => 'tourism', '2' => 'food party',     '3'     => 'south korean food', '4' => 'cooking', '5' => 'none of above'), 'data' => '5', 'expanded' => true, 'multiple' => false))  ->add('event2', 'choice', array('choices' => array('6' => 'cricket', '7' => 'football', '8' => 'hockey', '9' => 'baseball', '10' => 'polo', '5' => 'none of above'), 'data' => '5', 'expanded' => true, 'multiple' => false))  ->add('event3', 'choice', array('choices' => array('11' => 'game 1', '12' => 'game 2', '13' => 'game 3', '14' => 'game 4', '15' => 'game 5', '5' => 'none of above'), 'data' => '5', 'expanded' => true, 'multiple' => false))  ->add('register', 'submit'); }  public function getname() {  return 'subscriptions'; } } 

this controller "defaultcontroller"

 <?php   namespace instituteprojectevents\studentbundle\controller;   use symfony\bundle\frameworkbundle\controller\controller;  use instituteprojectevents\studentbundle\entity\subscriptions;  use instituteprojectevents\studentbundle\form\type\subscriptionstype;  use symfony\component\httpfoundation\request;   class defaultcontroller extends controller {  public function eventsoneaction(request $request) {   $subscriptions = new subscriptions();  //get logged in users id $user = $this->get('security.context')->gettoken()->getuser(); $userid = $user->getid();  //check if events selected user $repository = $this->getdoctrine()->getmanager()         ->getrepository('instituteprojecteventsstudentbundle:subscriptions');  $query = $repository->findoneby(array('id' => $userid));  if(($query == null)) {     $subscriptions->setevent1(5);     $subscriptions->setevent2(5);    $subscriptions->setevent3(5);     $subscriptions->setstudents($userid);     $form = $this->createform(new subscriptionstype(), $subscriptions);    $form->handlerequest($request);     }    else {         $subscriptions->setevent1($query->getevent1());        $subscriptions->setevent2($query->getevent2());        $subscriptions->setevent3($query->getevent3());         $subscriptions->setstudents($userid);        $form = $this->createform(new subscriptionstype(), $subscriptions);        $form->handlerequest($request);   }  if ($form->isvalid()) { //save database      $em = $this->getdoctrine()->getmanager(); $em->persist($subscriptions); $em->flush();    return $this->redirect($this->generateurl('instituteproject_events_student_eventsregistered')); }   if($current_date > date_format($date,"y/m/d h:i:s a")) {    return $this->render('instituteprojecteventsstudentbundle:default:registrationsclosed.html.twig');    }  else {       $form = $this->createform(new subscriptionstype(), $subscriptions);        return $this->render('instituteprojecteventsstudentbundle:default:eventsday1.html.twig', array('form' => $form ->createview()));  }  }  /**  * action displays confirmation page on success.  */ public function eventsregisteredaction() { return $this->render('instituteprojecteventsstudentbundle:default:eventsregistered.html.twig'); } } 

what validation needs written in "defaultcontroller.php" apply rule of selection of maximum of 2 sets of radio buttons , minimum of 0?

what applying callback constraint whole form fields?

...  public function setdefaultoptions(optionsresolverinterface $resolver) {     $resolver         ->setdefaults(array(             ...             'constraints' => array(                 new callback(                     array('callback' => array($this, 'validateform'))                 )             )         )); }  public function validateform($data, executioncontextinterface $context) {     if (condition) {         // build , add violation     } } 

alternatively can check request object..