Отправка формы ajax в PHP symfony 4

Я пытаюсь отправить форму с помощью ajax и отправить ее данные в базу данных, но я не понимаю, как обрабатывать данные, полученные от вызова ajax.

Я написал следующий код:

{% extends 'base.html.twig' %}

{% block title %}Assignments | CRM Fabriek{% endblock %}

{% block body %}

    <div class = "container">
        <div class = "columns">
            <div class = "column is-full">
                <div class = "level">
                    <h1 class = "level-left title title-no-margin is-vcentered">Assignments</h1>

                    <div class = "level-right">
                        {% include 'search.html.twig' %}

                        <a href = "{{ path("newAssignment") }}" class = "level-item button is-success">Add new</a>
                    </div>
                </div>
                <table class = "table is-fullwidth">
                    <tr>
                        <th>Name</th>
                        <th>Description</th>
                        <th>Status</th>
                        <th>Actions</th>
                    </tr>
                    {% if assignments != null %}
                        {% for assignment in assignments %}
                            <tr>
                                <td>{{ assignment.name }}</td>
                                <td>{{ assignment.description }}</td>
                                <td>{{ assignment.status }}</td>
                                <td>
                                    <a class = "button is-info is-small" href = "{{ path('overviewAssignment', {'id': assignment.id}) }}"><i class = "fa fa-eye"></i></a>
                                    <a class = "button is-warning is-small" href = "{{ path('editAssignment', {'id': assignment.id}) }}"><i class = "fa fa-pencil"></i></a>
                                    <button class = "button is-success is-small" onclick = "openModal({{ assignment.id }})"><i class = "fa fa-plus"></i></button>
                                </td>
                            </tr>
                        {% endfor %}
                    {% else %}
                        <tr>
                            <td colspan = "4">No entries</td>
                        </tr>
                    {% endif %}
                </table>
                <div class = "pagerfanta">
                    {{ pagerfanta(pager)}}
                </div>
                <div>
                    <div class = "modal">
                        <div class = "modal-background"></div>
                        <div class = "modal-card">
                            <header class = "modal-card-head">
                                <p class = "modal-card-title">Modal title</p>
                            </header>
                            <section class = "modal-card-body">
                                {{ form_start(form, {'attr': {'id': 'task_form'}}) }}
                                {{ form_row(form.name, {'attr': {'class': 'input'}}) }}
                                {{ form_row(form.description, {'attr': {'class': 'textarea'}}) }}

                                {{ form_label(form.status) }}
                                <div class = "control">
                                    <div class = "select">
                                        {{ form_widget(form.status) }}
                                    </div>
                                </div>

                                {{ form_end(form) }}
                            </section>
                            <footer class = "modal-card-foot">
                                <button id = "submit_task" class = "button is-success">Save changes</button>
                                <button class = "button" onclick = "closeModal()">Cancel</button>
                            </footer>
                        </div>
                    </div>
                </div>
            </div>
        </div>
    </div>

{% endblock %}

{% block javascripts %}
    <script>
        function openModal(id){
            $('.modal').addClass('is-active');
            $('#submit_task').attr('onClick', 'submitTask('+ id +');');
        }

        function closeModal(){
            $('.modal').removeClass('is-active');

        }
        function submitTask(id){
            console.info(id);

            form = $('#task_form').serialize();

            console.info(form); 
            $.ajax({
                url:'{{ path('submit_task') }}',
                type: "POST",
                dataType: "json",
                data: {
                    "task": form
                },
                async: true,
                success: function (return_data)
                {
                    console.info(return_data);
                },
                error: function (xhr, ajaxOptions, thrownError)
                {

                }
            });
            closeModal();
        }
    </script>
{% endblock %}

С помощью следующего метода в контроллере:

/**
     * @Route("/", name = "submit_task")
     */
    public function add_task(Request $request){
        $form_data = $request->get('task');

        return new JsonResponse($form_data);
    }

Форма создается в действии index:

/**
     * @Security("is_authenticated()")
     * @Route("/assignments", name = "assignments")
     */
    public function index(Request $request)
    {

        $assignment_rep = $this->getDoctrine()->getRepository(Assignment::class);

        if ($request->get('search') == null) {
            if ($this->get('security.authorization_checker')->isGranted('ROLE_ADMIN')){
                $assignments = $assignment_rep->findAll();
            }
            else
            {
                /* @var User $user */
                $user = $this->getUser();
                $assignments = array();
                foreach($user->getAssignments() as $assignment){
                    array_push($assignments, $assignment);
                }
            }
        }
        else{

            if ($this->get('security.authorization_checker')->isGranted('ROLE_ADMIN')){
                $assignments = $assignment_rep->search($request->get('search'));
            }
            else
            {
                /* @var User $user */
                $assignments = $assignment_rep->searchUser($request->get('search'), $this->getUser()->getId());
            }
        }

        $page = $request->query->get('page', 1);

        $adapter = new ArrayAdapter($assignments);

        $pagerfanta = new Pagerfanta($adapter);
        $pagerfanta->setMaxPerPage(25);
        $pagerfanta->setCurrentPage($page);


        $task = new Task();
        $form = $this->createForm(TaskFormType::class, $task);
        $form->remove('assignment');

        $assignments = $pagerfanta->getCurrentPageResults();

        return $this->render('assignment/index.html.twig', array(
            'assignments' => $assignments,
            'pager' => $pagerfanta,
            'form' => $form->createView()
        ));
    }

Я хотел бы знать, как обрабатывать данные формы без объекта «форма» в функции. Может ли кто-нибудь помочь мне с этой проблемой!