ExtraDataBundle/EventListener/SonataAdminConfigureListener.php

<?php

namespace ExtraDataBundle\EventListener;

use Sonata\AdminBundle\Event\ConfigureEvent;
use Symfony\Component\Form\Extension\Core\Type\TextareaType;

class SonataAdminConfigureListener
{

    /**
     * @param ConfigureEvent $event
     */
    public function addOptions(ConfigureEvent $event)
    {
        if ($event->getMapper()->has('extraData')) {
            $formMapper = $event->getMapper();
            $formMapper->add('extraData', TextareaType::class, array(
                    'required' => false,
                    'help' => 'help.json_format',
                ), array(
                    'translation_domain' => 'ExtraDataBundle',
                )
            );
        }
    }

    /**
     * @param ConfigureEvent $event
     */
    public function addTemplate(ConfigureEvent $event)
    {
        if ($event->getMapper()->has('extraData')) {
            $extraData = $event->getMapper()->get('extraData');
            $extraData->setTemplate('ExtraDataBundle:CRUD:extra_data_field.html.twig');
            $extraData->setOption('data', $event->getType());
            $extraData->setOption('translation_domain', 'ExtraDataBundle');
        }
    }

}