gistfile1.php

<?php

use Hateoas\HateoasBuilder;
use Hateoas\Configuration\Annotation as Hateoas;
use JMS\Serializer\Annotation as Serializer;
use JMS\Serializer\SerializerBuilder;
use JMS\Serializer\SerializationContext;

/**
 * @Serializer\ExclusionPolicy("all")
 */
class User
{

    /**
     * @Serializer\Expose
     */
    private $username;

    /**
     * @Serializer\Expose
     * @Serializer\MaxDepth(1)
     */
    private $friend;

    function __construct($username)
    {
        $this->username = $username;
    }

    public function getFriend()
    {
        return $this->friend;
    }

    public function setFriend($friend)
    {
        $this->friend = $friend;
    }

}

$foo    = new User('foo');
$bar    = new User('bar');
$foobar = new User('foobar');
$baz    = new User('baz');

$foo->setFriend($bar);
$bar->setFriend($foobar);
$foobar->setFriend($baz);

$serializer = SerializerBuilder::create()->build();

$json = $serializer->serialize($foo, 'json', SerializationContext::create()->enableMaxDepthChecks());