twig json_encode empty json

Question

I'm receiving a list of elements from an API. All the elements are well formatted. When I dump one of them using twig, I get the following :

Leg {#2695 ▼
-id: null
#reservation: null
-airportStart: "AIX LES MILLES"
-airplaneType: "Cessna Citation Mustang"
-airportEnd: "ROBINSON"
-startDate: "2015-09-10 20:00:00"
-startHour: "2015-09-10 20:00:00"
-endHour: "2015-09-10 21:00:21"
-durationLeg: "01:21"
#nbPax: "4"
-price: null
-updatedPrice: null
-discountOnLeg: null
-tva: null
-status: null
}

My user must select one of these elements, So what I'm trying to do is to send the encoded json back to the controller, using

{{ element|json_encode }}

Unfortunately, the json is empty. When I try to dump the encoded json using

{{ dump(element|json_encode) }}

all I get is an empty array {};

Any idea why Is there another way to send the selected element datas to a controller function? (These elements are not persisted, each call on the API returns thousands of results)

json_encode() only serializes the publicly visible properties of an object. — malcolm
– malcolm, Commented Sep 22, 2015 at 8:51

chebaby · Accepted Answer · 2017-10-21 21:23:46Z

I'm little late to the party (2 years of lateness), but for any one like me coming from a google research i say : i had the same problem too, and after googling around, i "solved" my problem with the Serializer Component. How? let me show you!

Installation

php composer.phar require symfony/serializer

Entity

<?php

namespace Your\Namespace\Entity;

use Doctrine\ORM\Mapping as ORM;
use Symfony\Component\Serializer\Serializer;
use Symfony\Component\Serializer\Encoder\JsonEncoder;
use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;

/**
 * Leg
 *
 * @ORM\Table()
 * @ORM\Entity(repositoryClass="Your\Namespace\Entity\LegRepository")
 */
class Leg {

    /**
     * @var integer
     *
     * @ORM\Column(name="id", type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $id;

    ...

    public function serializer()
    {
        $encoder    = new JsonEncoder();
        $normalizer = new ObjectNormalizer();

        $normalizer->setIgnoredAttributes(array(
            'whatever', 'attributes', 'you', 'want', 'to', 'ignore'
        ));

        // The setCircularReferenceLimit() method of this normalizer sets the number 
        // of times it will serialize the same object 
        // before considering it a circular reference. Its default value is 1.
        $normalizer->setCircularReferenceHandler(function ($object) {
            return $object->getName();
        });

        $serializer = new Serializer(array($normalizer), array($encoder));
        return $serializer->serialize($this, 'json');
    }
}

Twig

{{ Leg.serializer|raw }}

N.B : this is tested under symfony 2.6

just a small correction : for using to pass the object in javascript : <script> let leg = JSON.parse({{ Leg.serializer | json_encode | raw }})</script>

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