KnpUniversity Symfony REST: Using @link with the PaginatedCollection (http://knpuniversity.com/screencast/symfony-rest3/evaluating-expression)

Link.php

<?php

namespace AppBundle\Annotation;

/**
 * @Annotation
 * @Target("CLASS")
 */
class Link
{
    /**
     * @Required
     *
     * @var string
     */
    public $name;

    /**
     * @var string
     */
    public $route;

    public $params = array();

    /**
     * Instead of specifying route+params, you can just
     * specify the link directly
     *
     * @var string
     */
    public $url;
}

LinkSerializationSubscriber.php

<?php

namespace AppBundle\Serializer;

use AppBundle\Annotation\Link;
use Doctrine\Common\Annotations\Reader;
use JMS\Serializer\EventDispatcher\EventSubscriberInterface;
use JMS\Serializer\EventDispatcher\ObjectEvent;
use JMS\Serializer\JsonSerializationVisitor;
use Symfony\Component\ExpressionLanguage\ExpressionLanguage;
use Symfony\Component\Routing\RouterInterface;

class LinkSerializationSubscriber implements EventSubscriberInterface
{
    private $router;

    private $annotationReader;

    private $expressionLanguage;

    public function __construct(RouterInterface $router, Reader $annotationReader)
    {
        $this->router = $router;
        $this->annotationReader = $annotationReader;
        $this->expressionLanguage = new ExpressionLanguage();
    }

    public function onPostSerialize(ObjectEvent $event)
    {
        /** @var JsonSerializationVisitor $visitor */
        $visitor = $event->getVisitor();

        $object = $event->getObject();
        $annotations = $this->annotationReader
            ->getClassAnnotations(new \ReflectionObject($object));

        $links = array();
        foreach ($annotations as $annotation) {
            if ($annotation instanceof Link) {
                if ($annotation->url) {
                    $uri = $this->evaluate($annotation->url, $object);
                } else {
                    $uri = $this->router->generate(
                        $annotation->route,
                        $this->resolveParams($annotation->params, $object)
                    );
                }

                // allow a blank URI to be an optional link
                if ($uri) {
                    $links[$annotation->name] = $uri;
                }
            }
        }

        $visitor->addData('_links', $links);
    }

    private function resolveParams(array $params, $object)
    {
        foreach ($params as $key => $param) {
            $params[$key] = $this->evaluate($param, $object);
        }

        return $params;
    }

    private function evaluate($expression, $object)
    {
        return $this->expressionLanguage
            ->evaluate($expression, array('object' => $object));
    }

    public static function getSubscribedEvents()
    {
        return array(
            array(
                'event' => 'serializer.post_serialize',
                'method' => 'onPostSerialize',
                'format' => 'json',
            )
        );
    }
}

PaginatedCollection.php

<?php

namespace AppBundle\Pagination;
use JMS\Serializer\Annotation as Serializer;

use AppBundle\Annotation\Link;

/**
 * @Link(
 *      "self",
 *      url = "object.getUrl('self')"
 * )
 * @Link(
 *      "next",
 *      url = "object.getUrl('next')"
 * )
 * @Link(
 *      "prev",
 *      url = "object.getUrl('prev')"
 * )
 * @Link(
 *      "first",
 *      url = "object.getUrl('first')"
 * )
 * @Link(
 *      "last",
 *      url = "object.getUrl('last')"
 * )
 */
class PaginatedCollection
{
    private $items;

    private $total;

    private $count;

    /**
    * @Serializer\Exclude()
    * @var array
    */
    private $links = array();

    public function __construct(array $items, $totalItems)
    {
        $this->items = $items;
        $this->total = $totalItems;
        $this->count = count($items);
    }

    public function addLink($ref, $url)
    {
        $this->links[$ref] = $url;
    }

    public function getUrl($ref)
    {
        return isset($this->links[$ref]) ? $this->links[$ref] : '';
    }
}