Jak używać select box powiązanych z innym select box?

Miałem ten sam problem. Musisz użyć zdarzeń formularza. Mój przykład kodu z relacji kraju, regionu, miasta.

namespace Orfos\UserBundle\Form\Type;

///import form events namespace
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\Form\FormEvents;
use Symfony\Component\Form\Event\DataEvent;

class RegistrationFormType extends BaseType
{

    private $request;

    public function __construct($class, $request, $doctrine)
    {
        parent::__construct($class);
        $this->request = $request;
        $this->doctrine = $doctrine;
    }

    public function buildForm(FormBuilder $builder, array $options)
    {
        parent::buildForm($builder, $options);
        //other fields

        $locale = $this->request->getLocale();

        $builder->add('country', 'entity', array(
            'class' => 'Orfos\CoreBundle\Entity\Country',
            'property' => $locale . 'name',
            'label' => 'register.country.label',
            'query_builder' => function(EntityRepository $er) {
                return $er->createQueryBuilder('c')
                                ->select('c', 't')
                                ->join('c.translations', 't');
            },
        ));

        $factory = $builder->getFormFactory();
        $refreshRegion = function ($form, $country) use ($factory, $locale) {
                    $form->add($factory->createNamed('entity', 'region', null, array(
                                'class' => 'Orfos\CoreBundle\Entity\Region',
                                'property' => $locale . 'name',
                                'label' => 'register.region.label',
                                'query_builder' => function (EntityRepository $repository) use ($country) {
                                    $qb = $repository->createQueryBuilder('region')
                                            ->select('region', 'translation')
                                            ->innerJoin('region.country', 'country')
                                            ->join('region.translations', 'translation');

                                    if ($country instanceof Country) {
                                        $qb = $qb->where('region.country = :country')
                                                ->setParameter('country', $country);
                                    } elseif (is_numeric($country)) {
                                        $qb = $qb->where('country.id = :country_id')
                                                ->setParameter('country_id', $country);
                                    } else {
                                        $qb = $qb->where('country.id = 1');
                                    }

                                    return $qb;
                                }
                            )));
                };
        $factory = $builder->getFormFactory();
        $refreshCity = function($form, $region) use ($factory, $locale) {
                    $form->add($factory->createNamed('entity', 'city', null, array(
                                'class' => 'Orfos\CoreBundle\Entity\City',
                                'property' => $locale . 'name',
                                'label' => 'register.city.label',
                                'query_builder' => function (EntityRepository $repository) use ($region) {
                                    $qb = $repository->createQueryBuilder('city')
                                            ->select('city', 'translation')
                                            ->innerJoin('city.region', 'region')
                                            ->innerJoin('city.translations', 'translation');

                                    if ($region instanceof Region) {
                                        $qb = $qb->where('city.region = :region')
                                                ->setParameter('region', $region);
                                    } elseif (is_numeric($region)) {
                                        $qb = $qb->where('region.id = :region_id')
                                                ->setParameter('region_id', $region);
                                    } else {
                                        $qb = $qb->where('region.id = 1');
                                    }

                                    return $qb;
                                }
                            )));
                };

        $builder->addEventListener(FormEvents::PRE_SET_DATA, function (DataEvent $event) use ($refreshRegion, $refreshCity) {
                    $form = $event->getForm();
                    $data = $event->getData();

                    if ($data == null){
                        $refreshRegion($form, null);
                        $refreshCity($form, null);
                    }

                    if ($data instanceof Country) {
                        $refreshRegion($form, $data->getCountry()->getRegions());
                        $refreshCity($form, $data->getRegion()->getCities());
                    }
                });

        $builder->addEventListener(FormEvents::PRE_BIND, function (DataEvent $event) use ($refreshRegion, $refreshCity) {
                    $form = $event->getForm();
                    $data = $event->getData();

                    if (array_key_exists('country', $data)) {
                        $refreshRegion($form, $data['country']);
                    }
                    if (array_key_exists('region', $data)) {
                        $refreshCity($form, $data['region']);
                    }                    
                });
    }

}

Można utworzyć akcję, która będzie zwracać tablicę json z pracownikami firmy. Po zmianie listy firm musisz zażądać tej akcji przez ajax i utworzyć select list of employees.

Form controller action:

/**
 * @Route("/job", name="_demo_job")
 * @Template()
 */
public function jobAction()
{
    $form = $this->createForm(new JobType());

    $request = $this->getRequest();
    if ($request->getMethod() == 'POST') {
        $form->bindRequest($request);
        $data = $form->getData();
        // some operations with form data
    }

    return array(
        'form' => $form->createView(),
    );
}

Conroller, który zwraca pracowników przez firmę w json:

/**
 * Finds all employees by company
 *
 * @Route("/{id}/show", name="employees_by_category")
 */
public function listByCompanyAction($id)
{
    $request = $this->getRequest();

    if ($request->isXmlHttpRequest() && $request->getMethod() == 'POST') {
        $em = $this->getDoctrine()->getEntityManager();

        $company = $em->getRepository('AcmeDemoBundle:Company')->find($id);

        // create array for json response
        $empoloyees = array();
        foreach ($company->getEmployees() as $employee) {
            $empoloyees[] = array($employee->getId(), $employee->getName());
        }

        $response = new Response(json_encode($empoloyees));
        $response->headers->set('Content-Type', 'application/json');

        return $response;
    }
    return new Response();
}

Szablon formularza:

<script type="text/javascript">
    $(document).ready(function() {
        $('#form_company').change(function() {
            var companyId = $(this).val();
            $.post('{{ route }}/' + companyId + '/show', function(data) {
                // last selected employee
                var selectedVal = $('option:selected', '#form_employee').attr('value');

                $('#form_employee option').remove();
                for (i in data) {
                    // create option with employee
                    var option = $('<option></option>').
                        attr('value', data[i][0]).
                        text(data[i][1]);
                    // set selected employee
                    if (data[i][0] == selectedVal) {
                        option.attr('selected', 'selected');
                    }
                    // append to employee to employees select
                    $('#form_employee').append(option);
                }
            }, 'json');
        })

        // request employees by company
        $('#form_company').change();
    })

</script>

<form action="{{ path('_demo_job') }}" method="post" {{ form_enctype(form) }}>
    {{ form_widget(form) }}

    <input type="submit" />
</form>

Aby uzyskać bardziej szczegółowy przykład, powinieneś opisać swój problem bardziej szczegółowo.