Access to variable in controller and render - php

Question

I have on my form template new.html.twig a select where all the elements of an entity are loaded ($categories).
Controller
public function newAction(Request $request){
$entity = new Playlist();
$form = $this->createCreateForm($entity);
$em = $this->getDoctrine()->getManager();
$categories = $em->getRepository('PublicartelAppBundle:Category')->getAllCategories();**
return $this->render('PublicartelAppBundle:Playlist:new.html.twig', array(
'categories' => $categories,
'entity' => $entity,
'form' => $form->createView(),
));
}
Select filter that serves to make a search.
Select in my twig template that displays all categories obtained from the query.
new.html.twig
<div class="form-group">
<label for="publicartel_appbundle_category_name">Search for category: </label>
<select id='selectCategory' class="form-control select2">
{% for category in categories %}
<option>
{{ category.name }}
</option>
{% endfor %}
</select>
</div>
JS in my twig template that detects changes in select option to make a new query and retrieve records from the selected option.
JS code
$('#selectCategory').on('change', function () {
var optionSelect = $(this).val();
$.post("{{path('playlist_category') }}", {category: optionSelect},
function (filterContent) {
for (var content in filterContent.category_result) {
for (var name in filterContent.category_result[content]) {
var result = filterContent.category_result[content][name];
console.log(result);
$('#playlist_content_name').append('<option>' + result + '</option>');
}
}
}, 'json');
});
The result of the new query is done in the playlist_category route is assigned to another select this in my twig template with the append method.
<div class="form-group">
<label for="publicartel_appbundle_area_name">Content</label>
{{ form_widget(form.items.vars.prototype.content, { 'id': 'playlist_content_name', 'full_name': '', required: false, 'attr': {'class': 'form-control select2'}}) }}
</div>
This select load other options, but the other select is used to filter options to prevent all options be loaded.
My problem is that when I try to send the form with any of the options obtained from the search, I get an error that the variable categories does not exist in my template twig new.html.twig.
Then, as the method createAction, also conducts a rendering of the template new.html.twig also add the variable $ categories there.
Controller
public function createAction(Request $request){
$entity = new Playlist();
$form = $this->createCreateForm($entity);
$form->handleRequest($request);
$em = $this->getDoctrine()->getManager();
if ($form->isValid()) {
// $em = $this->getDoctrine()->getManager();
$em->persist($entity);
$em->flush();
return $this->redirect($this->generateUrl('playlist_show', array(
'id' => $entity->getId())));
}
$categories = $em->getRepository('PublicartelAppBundle:Category')->getAllCategories();
return $this->render('PublicartelAppBundle:Playlist:new.html.twig', array(
'categories' => $categories,
'entity' => $entity,
'form' => $form->createView(),
));
}
But when complete the form, having chosen an option of select which return the search, instead of addressing the playlist_show route, directs me to the path /create with the form new.html.twig.