Set Default value of choice field Symfony FormType

Question

I want from the user to select a type of questionnaire, so I set a select that contains questionnaires types.

Types are loaded from a an entity QuestionType

Answer 1

The accepted answer of setting in the model beforehand is a good one. However, I had a situation where I needed a default value for a certain field of each object in a collection type. The collection has the allow_add and allow_remove options enabled, so I can't pre-instantiate the values in the collection because I don't know how many objects the client will request. So I used the empty_data option with the primary key of the desired default object, like so:

class MyChildType
extends AbstractType 
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder->add('optionalField', 'entity', array(
            'class' => 'MyBundle:MyEntity',
            // Symfony appears to convert this ID into the entity correctly!
            'empty_data' => MyEntity::DEFAULT_ID,
            'required' => false,
        ));
    }
}

class MyParentType
extends AbstractType 
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder->add('children', 'collection', array(
            'type' => new MyChildType(),
            'allow_add' => true
            'allow_delete' => true,
            'prototype' => true,  // client can add as many as it wants
        ));
    }
}