interface HydratorInterface
{
    /**
     * Extrait les valeurs de l'objet
     */
    public function extract($object);

    /**
     * Hydrate $object avec les valeurs dans $data
     */
    public function hydrate(array $data, $object);
}

class Foo
{
    public $a = 'bar';
}

$hydrator = new \Zend\Stdlib\Hydrator\ObjectProperty();
var_dump($hydrator->extract(new Foo()));

// Affiche : array('a' => 'bar');

class Foo
{
    public $a = 'bar';
}

$hydrator = new \Zend\Stdlib\Hydrator\ObjectProperty();
$object   = $hydrator->hydrate(array('a' => 'baz'), new Foo());
var_dump($object);

// Affiche object(Foo)[201]
//             public 'a' => string 'baz' (length=3)

namespace Application\Entity;

class Groupe
{
    /** @var string */
    public $nom;

    /** @var string */
    public $site;
}

namespace Application\Entity;

class Concert
{
    /** @var Groupe */
    public $groupe;

    /** @var int */
    public $nombreSieges;
}

namespace Application\Form;

use Application\Entity\Groupe;
use Zend\Form\Fieldset;
use Zend\Stdlib\Hydrator\ObjectProperty;

class GroupeFieldset extends Fieldset
{
    public function __construct()
    {
        parent::__construct('groupe');

        $this->setObject(new Groupe())
             ->setHydrator(new ObjectProperty());

        // Ajout des éléments...
        […]
    }
}

// Dans GroupeFieldset::__construct
$this->add(array(
    'name'    => 'nom',
    'options' => array(
        'label' => 'Nom'
    )
));

$this->add(array(
    'type'    => 'Zend\Form\Element\Url',
    'name'    => 'site',
    'options' => array(
        'label' => 'Site web'
    )
));

$this->add(array(
    'name' => 'site',
    'options' => array(
        'label' => 'Site web'
    ),
    'attributes' => array(
        'required'   => 'required',
        'placeholder => 'http://'
    )       
));

use Zend\InputFilter\InputFilterProviderInterface;

class GroupeFieldset extends Fieldset 
    implements InputFilterProviderInterface
{
    public function getInputFilterSpecification()
    {
        return array(
            'nom' => array(
                'required'   => true,
                'filters'    => array(
                    array('name' => 'StringTrim')
                ),
                'validators' => array(
                    array('name' => 'StringLength', array('max' => 48))
                )
            )
        );
    }
}

class ConcertFieldset extends Fieldset
{
    public function __construct()
    {
        parent::__construct('concert');

        $this->setObject(new Concert())
             ->setHydrator(new ObjectProperty());

        // Ajout des éléments
        […]
    }
}

// Dans ConcertFieldset::construct__()
$this->add(array(
    'type'    => 'Application\Form\GroupeFieldset',
    'name'    => 'groupe',
    'options' => array(
        'label' => 'Groupe'
    )
));

$this->add(array(
    'type'    => 'Zend\Form\Element\Number',
    'name'    => 'nombreSieges',
    'options' => array(
        'label' => 'Nombre de sièges dans la salle'
    ),
    'attributes' => array(
        'min' => 50
    )
));

namespace Application\Form;

use Zend\Form\Form;
use Zend\Stdlib\Hydrator\ObjectProperty;

class CreerConcert extends Form
{
    public function __construct()
    {
        parent::__construct('creer-concert-form');

        $this->setHydrator(new ObjectProperty());

        // Ajout des éléments
        […]
    }
}

// Dans Application\Form\CreerConcert::__construct
$this->add(array(
    'type'    => 'Application\Form\ConcertFieldset',
    'name'    => 'concert',
    'options' => array(
        'use_as_base_fieldset' => true
    )
));

$this->add(array(
    'type'       => 'Zend\Form\Element\Submit',
    'name'       => 'submit',
    'attributes' => array(
        'value' => 'Créer ce concert !',
        'class' => 'btn-success'
    )
));

// dans application/create-concert.phtml
$form = $this->form;
$form->setAttribute('action', $this->url(null, array(), true))
     ->prepare();

$concert = $form->get('concert');
$groupe  = $concert->get('groupe');

echo $this->form()->openTag($form); // <form action="…">

echo $this->formLabel($concert->get('nombreSieges'));
echo $this->formNumber($concert->get('nombreSieges'));
echo $this->formElementErrors($concert->get('nombreSieges'));

echo $this->formRow($groupe->get('nom'));
echo $this->formRow($groupe->get('site'));

echo $this->formSubmit($form->get('submit'));

echo $this->form()->closeTag($form); // </form>

public function createConcertAction()
{
    $form = new CreerConcert();

    if ($this->request->isPost()) {
        $concert = new Concert();
        $form->bind($concert);
        $form->setData($this->request->getPost());

        if ($form->isValid()) {
            var_dump($concert);
        }
    }

    return new ViewModel(array(
        'form' => $form
    ));
}

class UpdateConcert extends Form
{
    public function __construct()
    {
        parent::__construct('update-concert-form');

        $this->setHydrator(new ObjectProperty());

        $this->add(array(
            'type'    => 'Application\Form\ConcertFieldset',
            'name'    => 'concert',
            'options' => array(
                'use_as_base_fieldset' => true
            )
        ));

        $this->setValidationGroup(array(
            'concert' => array( 'nombreSieges')
        ));

public function updateConcertAction()
{
    $form = new UpdateConcert();
    $concert = [...]; // récupère de la base de données par exemple
    $form->bind($concert);

    if ($this->request->isPost()) {
        $form->setData($this->request->getPost());

        if ($form->isValid()) {
            var_dump($concert);
        }
    }

    return new ViewModel(array(
        'form' => $form
    ));
}