Form PatchSubsciber for Symfony 2.3. This Form Event Subscriber will help prepare data for a PATCH request. It can be added in your CustomFormType::buildForm method.

gistfile1.php

<?php

namespace Acme\DemoBundle\EventSubscriber;

use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\Form\FormEvents;
use Symfony\Component\Form\FormEvent;

/**
 * Changes Form->submit() behavior so that it treats not set values as if they
 * were sent unchanged.
 *
 * Use when you don't want fields to be set to NULL when they are not displayed
 * on the page (or to implement PUT/PATCH requests).
 * @link https://gist.github.com/makasim/3720535 for more information
 */
class PatchSubscriber implements EventSubscriberInterface
{
    public function onPreSubmit(FormEvent $event)
    {
        $form = $event->getForm();
        $clientData = $event->getData();
        $clientData = array_replace($this->prepareData($form), $clientData ?: array());
        $event->setData($clientData);
    }

    /**
     * Returns the form's data like $form->submit() expects it
     */
    protected function prepareData($form)
    {
        if ($form->count()) {
            $data = array();
            foreach ($form->all() as $name => $child) {
                $data[$name] = $this->prepareData($child);
            }
            return $data;
        } else {
            return $form->getViewData();
        }
    }

    static public function getSubscribedEvents()
    {
        return array(
            FormEvents::PRE_SUBMIT => 'onPreSubmit',
        );
    }
}

To use this code add the event subscriber in your custom form type like this:

<?php 
// Acme/DemoBundle/Form/Type/CustomFormType.php
namespace Acme\DemoBundle\Form\Type;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;

class CustomFormType extends AbstractType
{
    // ...

    public function buildForm(FormBuilderInterface $builder, array $options) 
    {
        // your logic here ...

        if($options['method'] === 'PATCH') {
            // Event Subscriber to prepare the submitted data for a PATCH
            $builder->addEventSubscriber(new PatchSubscriber());
        }
    }
}

Hey, thank you for the patch. $options['method'] is always "POST" here. Nevertheless, I kicked this condition, because I dont need it. Thanks again.

Hi, thank you for this patch it's been very useful. However, I've had a little problem with boolean field, rendered as a checkbox. When unchecked, to set the field to false, it's considered empty and then replaced by the patch and set to true. Am I missing somehting, how can I deal with that?

Thank you