Implemented a PUT endpoint in Zend Framework 2

use Zend\Mvc\Controller\AbstractRestfulController;
use Zend\View\Model\JsonModel;

class BeerRestController extends AbstractRestfulController {

  /** @var \Doctrine\ORM\EntityManager */
  private $em;

  /** @var \Doctrine\ORM\EntityRepository */
  private $beerRepo;

  /** @var \JMS\Serializer\Serializer */
  private $serializer;

  public function __constructor() {
    $sm = $this->getServiceLocator();

    // You'll have to configure these services in your module
    $this->em = $sm->get('doctrine.entitymanager.orm_default');
    $this->beerRepo = $this->em->getRepository('MyApp\Model\Beer');

    $this->serializer = $sm->get('jms_serializer');
  }

  /** GET /beers/:id */
  public function get($id) {
    // Use Doctrine ORM to create a beer model
    // from a db record with a matching id.
    $beer = $this->beerRepo->findById($id);

    // Serialize the MyApp\Model\Beer model into json,
    // and send it back to the client
    $beerJson = $this->serializer->serialize($beer, 'json');

    return new JsonModel(json_decode($beerJson));
    // JsonModel expects a php array (not a json string),
    // so we have to re-deserialize the json into a plain array.
    // I'll show you in the next post how to abstract this out, so you
    // don't have to do this every time.
  }

  /** POST /beers */
  public function create($data) {
    // Create a MyApp\Model\Beer model from
    // the client's json request
    $beerJson = json_encode($data);
    $beer = $this->serializer->deserialize($beerJson, 'MyApp\Model\Beer', 'json');

    // Save the beer to the db
    $this->em->persist($beer);
    $this->em->flush();

    // Send the updated beer model (with id) back to the client.
    $updatedBeerJson = $this->serializer->serialize($beer, 'json');
    return new JsonModel(json_decode($updatedBeerJson));
  }

}

class BeerRestController extends AbstractRestController {
// ...

  /** PUT /beers/:id */
  public function update($id, $data) {
    // Create a beer model from the client's data
    $updatedBeer = $this->serializer->deserialize(json_encode($data), 'MyApp\Model\Beer', 'json');

    // Merge the client's beer model with the existing model
    $this->em->merge($updatedBeer);
    $this->em->flush();

    // Send the updated beer model (with id) back to the client.
    $updatedBeerJson = $this->serializer->serialize($beer, 'json');
    return new JsonModel(json_decode($updatedBeerJson));
  }

}

class BeerRestController extends AbstractRestController {
// ...

  /** PUT /beers/:id */
  public function update($id, $data) {
    /**
     * User passes in some new data for a beer model.
     * $data = array(
     *   'id' => 123,
     *   'ibu' => 70
     * );
     */

    $updatedBeer = $this->serializer->deserialize(json_encode($data), 'MyApp\Model\Beer', 'json');
    /**
     * JMS Serializer coverts the raw data into a Beer model,
     * with some missing fields:
     *
     * object(MyApp\Model\Beer)
     *  'id' => 1
     *  'name' => null
     *  'brewery_id' => null
     *  'ibu' => 70
     *  'abv' => null
     */

    $this->em->merge($updatedBeer);
    $this->em->flush();
    /**
     * Doctrine updates the existing beer model
     * with any defined fields in the $updatedBeerModel,
     * including the fields which are set to null.
     *
     * Saving null fields to the db makes MySQL angry,
     * and everything comes crashing down.
     */

    // ...
  }

}

  // ...
  $data = array(
    'id' => 123,
    'ibu' => 70
  );
  $beer = $this->beerRepo->findById(123);

  // Deserialize our data "on top of" an existing beer model,
  // only updating fields defined in the json object.
  $this->serializer->deserialize($data, $beer, 'json');

  $this->em->persist($beer);

$objectConstructor = new InitializedObjectConstructor(new UnserializeObjectConstructor());

// module.config.php
// ...
    'service_manager' => array(
      'factories' => array(
        // Create a jms serializer service,
        // configured to use the InitializedObjectConstructor
        'serializer' => function() {
          // ...
          $defaultObjCtor = new \JMS\Serializer\Construction\UnserializeObjectConstructor();
          $initializedObjCtor = new \MyApp\path\to\copy\and\pasted\InitializedObjectCtor($defaultObjCtor);

          return \JMS\Serializer\SerializerBuilder::create()
            ->setObjectConstructor($initializedObjCtor)
            ->build();
        }
      ),
    ),
// ...

  /** PUT /beers/:id */
public function update($id, $data) {
  // Create a deserialization context, targeting the existing beer model
  $context = new \JMS\Serializer\DeserializationContext();
  $context->attributes->set('target', $user);

  // Deserialize the data "on to" to the existing beer model
  $this->serializer->deserialize(json_encode($data), 'MyApp\Model\Beer', 'json', $context);

  // Save the updated beer model
  $this->em->persist($updatedBeer);
  $this->em->flush();

  // ...
}