Symfony2 form populating entitiy based on other entity - forms

Question

I'm using Symfony2 form component to create and modify forms. I'm currently loading all model entities as choices, but I need to get only the Models related to the selected (posted) value from manufacturer.
How can I achieve this?
class VehicleType extends AbstractType
{
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder->add('manufacturer', 'entity', array(
'label' => 'Brand',
'attr' => array('class' => 'input-block-level'),
'class' => 'BalslevCarBundle:Manufacturers',
'property' => 'short_name',
'empty_value' => 'All',
'required' => false
));
$builder->add('model', 'entity', array(
'label' => 'Model',
'class' => 'BalslevCarBundle:Models',
'property' => 'model',
'empty_value' => 'All',
'required' => false
));
}
public function getName()
{
return 'search';
}
}

Answer 1

First of all, you have to create "dynamically" your choices based onto user selection.
There are two ways, strictly coupled with your application behaviour, that leads (in both cases) at the same "core" code; the difference is only the way you call it.
So, let's explain the two possibilities:
Select manufacturer "statically" and don't change it over the time of request: use data retrieved from your business logic
Select manufacturer "dinamically" and can change them over the time of request: replace your form at every request; new form will be provided by business logic
So, the HEART of your question is: how can I retrieve only associated entities?
Answer
Into your VehicleType.php (where entity, in this case, is VehicleType ?)
private $manufacturerId;
public function __construct($manufacturerId)
{
$this->manufacturerId = $manufacturerId;
}
public function BuildForm(FormBuilderInterface $builder)
{
$manufacturerId = $this->manufacturerId;
$manufacturerQuery = function(EntityRepository $repo) use ($manufacturerId ){
return $repo->createQueryBuilder('m')
->where('m.id = :id')
->setParameter('id',$manufacturerId );};
$builder->add('manufacturer', 'entity', array(
'label' => 'Brand',
'attr' => array('class' => 'input-block-level'),
'class' => 'BalslevCarBundle:Manufacturers',
'property' => 'short_name',
'empty_value' => 'All',
'required' => false,
'query_builder' => $manufacturerQuery;
));
$builder->add('model', 'entity', array(
'label' => 'Brand',
'attr' => array('class' => 'input-block-level'),
'class' => 'BalslevCarBundle:Manufacturers',
'property' => 'short_name',
'empty_value' => 'All',
'required' => false,
'query_builder' => $modelQuery;
));
}
As you can see, in this way we use a custom repository to get only entities that are suitable for our needs. Obviously I am writing my DQL query without knowing your DB structure: it's your task and responsibility to adapt it to your real situation.
Moreover, you have to create another query for model (called $modelQuery in my answer) to retrieve correct models based on selected $id