updating student information in symfony - ajax

Question

I am developping an application and I got a problem in my front-end part. It's related to Symfony and Ajax. So I am using a session variable in order to add a student to a school before sending the form of school to the server (back-end). I am using then some Ajax. I do not how to debug it. I tried what it is posted in the net but it does not work. I was able to add a student to a school but I was not able to update the student information. That's seem easy but it's not as I thought. Here is an ajax call that I am using in my SchoolCreate.html.twig:
function ajax () {
$.ajax({
type: 'POST',
url: "{{ path('student_add') }}",
data: $('#addStudent').serialize(),
success: function (response) {
var htmlToDisplay = response.trim();
$('#students').html(htmlToDisplay);
}
});
}
My modal used to create school:
<div class="modal-body">
{{ render(controller('AppBundle:School:addStudent')) }}
</div>
addStudent:
public function addStudentAction(Request $request) {
$student = new Student();
$form = $this->createForm(StudentType::class, $student);
$form->handleRequest($request);
$headers = array('Accept' => 'application/json');
$encoders = array(new JsonEncoder());
$normalizers = array(new ObjectNormalizer());
$serializer = new Serializer($normalizers, $encoders);
if ($request->isXmlHttpRequest())
{
$session = $request->getSession();
$student = $form->getData();
if ($session->has('students'))
$students = $session->get('students');
$students[] = $student;
$session->set('$students', $students);
$template = $this->renderView('AppBundle:School:StudentList.html.twig', array(
'students' => $students
));
return new Response($template);
}
return $this->render('AppBundle:Student:StudentAdd.html.twig', array(
'form' => $form->createView()
));
}
I try to do the same in updateStudent function but I got a problem related to 30 second exceeded and I do not know how to debug in Ajax. I define my bottom of update inside StudentList.html.twig
Thanks,