Return a JSON array from a Controller in Symfony

I think the @darkangelo answer need explainations.

The findAll() method return a collection of objects.

$categorias = $this->getDoctrine()
                   ->getRepository('AppBundle:Categoria')
                   ->findAll();

To build your response, you have to add all getters of your entities to your response like :

$arrayCollection = array();

foreach($categorias as $item) {
     $arrayCollection[] = array(
         'id' => $item->getId(),
         // ... Same for each property you want
     );
}

return new JsonResponse($arrayCollection);

Use QueryBuilder allows you to return results as arrays containing all properties :

$em = $this->getDoctrine()->getManager();
$query = $em->createQuery(
    'SELECT c
    FROM AppBundle:Categoria c'
);
$categorias = $query->getArrayResult();

return new JsonResponse($categorias);

The getArrayResult() avoids need of getters.

You need to do this (based on previous answer):

public function getAllCategoryAction() {
    $em = $this->getDoctrine()->getManager();
    $query = $em->createQuery(
        'SELECT c
        FROM AppBundle:Categoria c'
    );
    $categorias = $query->getArrayResult();

    $response = new Response(json_encode($categorias));
    $response->headers->set('Content-Type', 'application/json');

    return $response;
}

It works perfect with any Query that Doctrine returns as array.

/**
 * @Route("/api/list", name="list")
 */
public function getList(SerializerInterface $serializer, SomeRepository $repo): JsonResponse
{
    $models = $repo->findAll();
    $data = $serializer->serialize($models, JsonEncoder::FORMAT);
    return new JsonResponse($data, Response::HTTP_OK, [], true);
}