Webb-On-The-Webb.com

(I am operating under the assumption that the reader is already
familiar with the Symfony2 Form Component and Doctrine.
If not, you can read up on it here. )

The concept is simple. We have two HTML SELECT fields, one for
the city and one for the state (US). When the state is changed,
we would like to populate the city select with cities from the
selected state. We’ll use my ContactInfoType as an example.The
form type would look like this:

public function buildForm(FormBuilder $builder, array $options) {
    $builder->add('city', 'entity', array('query_builder' => function (EntityRepository $er) { ... }));
    $builder->add('state', 'entity', array('query_builder' => function (EntityRepository $er) { ... }));
}

Here is the relevant snippet from the Controller:

$em = $this->get('doctrine.orm.entity_manager');

// In beta2 the Entity Manager is retrieved by $this->get('doctrine')->getEntityManager();

$contact = $em->getRepository('Entity:ContactInfo')
 ->find(1);   $form = $this->get('form.factory')
 ->create(new ContactInfoType(), $contact)
 ->getForm();

if($this->get('request')->getMethod() == 'POST') {
    $form->bindRequest($this->get('request');

    $em->persist($contact);
    $em->flush();
}

Everything looks straightforward enough, but the solution is
flawed. Let’s say out $contact’s city is Columbia, MO. When
we instantiate our form in the Controller, the “city” field is
populated with cities in Missouri. Now we want to set the
city to Boulder, CO. We issue out our AJAX request and
retrieve a list of cities in Colorado and populate the “city”
SELECT accordingly, select Boulder and submit the form.
Now, back in our Controller, we reload our $contact form
the database and instantiate our form. Once again, our
“city” field is populated with cities in Missouri. Since this is
now a POST request, we want to bind the request to the
form. When the Form Component tries to setCity, the city
it is trying to set is not on the list, and that’s a problem.
I posted my issue on the Symfony Users mailing list, and
Berhard Schussek was kind enough to offer this solution.
It’s not the shortest solution in the world, but it works. To
work around this we need to use the Event System, utilizing
the “preSetData” and “preBind” events, and create a Closure
to use as a callback to create and populate the “city” field.
Before the data is set, we populate our “city” field with
cities in Missouri and then, before we bind data, we
re-create our “city” field, populating it with cities from
Colorado.
Here is our Closure:

$refreshCity = function ($form, $state) use ($factory) {
    $form->add($factory->createNamed('entity', 'city', null, array(
        'class'         => 'Entity:Cities',
        'property'      => 'city_name',
        'label'         => 'City',
        'query_builder' => function (EntityRepository $repository) use ($state) {
                               $qb = $repository->createQueryBuilder('cities')
                                                ->select(array('cities', 'zip_codes'))
                                                ->innerJoin('cities.states', 'states')
                                                ->innerJoin('cities.zip_codes', 'zip_codes');

                               if($state instanceof States) {
                                   $qb = $qb->where('cities.states = :state')
                                            ->setParameter('state', $state);
                               } elseif(is_numeric($state)) {
                                   $qb = $qb->where('states.state_id = :state_id')
                                            ->setParameter('state_id', $state);
                               } else {
                                   $qb = $qb->where('states.state_id = 1');
                               }

                               return $qb;
                           }
         )));
};

And now, let’s put $refreshCity to use:

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

 if($data == null)
    return;  //As of beta2, when a form is created setData(null) is called first

 if($data instanceof ContactInfo) {
 $refreshCity($form, $data->getCity()->getState());
 }
 });

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

 if(array_key_exists('state', $data)) {
 $refreshCity($form, $data['state']);
 }
});

Now we can use the ContactInfoType in our Controller and we
get the result we expect. This may be a somewhat lengthy
solution, but Symfony provides lots of opportunities for code
re-use. I use this form type in a *lot* of places and copy and
paste elsewhere.