symfony 3 doctrine one to one uni-direction returning unwanted fields when querying

I have got two classes which are being associated using one to one uni-direction

{
 id: 1,
 name: "onetooneuniparent name",
 onetooneunichild: {
   id: 1,
   name: "onetooneunichild name",
   __initializer__: null,
   __cloner__: null,
   __isInitialized__: true
  }
}

the above is the result when I do query like following

http://localhost:8000/onetooneRead?id=1

I want to know where and why the following come from

__initializer__: null,
__cloner__: null,
__isInitialized__: true

my expected result is just this

{
 id: 1,
 name: "onetooneuniparent name",
 onetooneunichild: {
   id: 1,
   name: "onetooneunichild name"
  }
}

OnetoOneUniParent.php

namespace AppBundleEntity;

use DoctrineORMMapping as ORM;

/**
 * @ORMEntity
 * @ORMTable(name="onetooneuniparent")
 */

class OnetoOneUniParent{

/**
 * @ORMColumn(type="integer")
 * @ORMId
 * @ORMGeneratedValue(strategy="AUTO")
 */
private $id;

/**
 * @ORMColumn(type="string",name="name")    
 */
private $name;

/**  
 * @ORMOneToOne(targetEntity="OnetoOneUniChild",cascade={"persist"})
 * @ORMJoinColumn(name="child_id", referencedColumnName="id")
 */
private $onetooneunichild;

<.... getter and setter here ...>
}

OnetoOneUniChild.php

namespace AppBundleEntity;

use DoctrineORMMapping as ORM;

/**
 * @ORMEntity
 * @ORMTable(name="onetooneunichild")
 */
 class OnetoOneUniChild{

/**
 * @ORMColumn(type="integer")
 * @ORMId
 * @ORMGeneratedValue(strategy="AUTO")
 */
private $id;

/**
 * @ORMColumn(type="string",name="name")    
 */
private $name;

<.... getter and setter here ...>

This is the method in controller

/**
 * @Route("/onetooneRead")
 * @Method("GET")
 */
public function onetooneReadAction(Request $request){
    $logger = $this->get('logger');
    $encoders = array(new XmlEncoder(), new JsonEncoder());
    $normalizers = array(new ObjectNormalizer());

    $serializer = new Serializer($normalizers, $encoders);

    $logger->info('onetoone Read');

    $id = $request->query->get("id");

    $em = $this->getDoctrine()->getManager();
    $onetooneuniparent = $em->getRepository('AppBundle:OnetoOneUniParent')->find($id);

    $onetooneuniparentJson = $serializer->serialize($onetooneuniparent, 'json');

    $response = new JsonResponse();

    $response->setContent($onetooneuniparentJson);

    return $response;   
}

This is what is inside in MySQL

mysql> select * from onetooneuniparent;
+----+----------+------------------------+
| id | child_id | name                   |
+----+----------+------------------------+
|  1 |        1 | onetooneuniparent name |
|  2 |        2 | onetooneuniparent name |
|  3 |        3 | onetooneuniparent name |
+----+----------+------------------------+
3 rows in set (0.00 sec)

mysql> select * from onetooneunichild;
+----+-----------------------+
| id | name                  |
+----+-----------------------+
|  1 | onetooneunichild name |
|  2 | onetooneunichild name |
|  3 | onetooneunichild name |
+----+-----------------------+
3 rows in set (0.00 sec)


Source: stackoverflow-php