Symfony Custom Form Type, based on: - https://github.com/liip/LiipFormTranslationChoiceBundle/blob/master/Form/Type/TranslationChoiceType.php - http://stackoverflow.com/questions/13344915/entity-mapping-in-a-symfony2-choice-field-with-optgroup

FormFieldController.php

<?php

namespace Acme\AuditBundle\Controller;

use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Symfony\Component\HttpFoundation\Request;
use Acme\AuditBundle\Entity\AuditFormField;
use Acme\AuditBundle\Entity\AuditFormSection;
use Acme\AuditBundle\Form\Type\AuditFormFieldType;

class AuditFormFieldController extends Controller
{
...
    /**
     * Edit existing field or create new field
     *
     * @param \Symfony\Component\HttpFoundation\Request $request
     *
     * @return twig template
     */
    public function editAction( Request $request )
    {
        ...
        $field = new AuditFormField();
        $form = $this->createForm( new AuditFormFieldType(), $field, array(
            'section' => $field->getSection(),
        ));
        ...

        return $this->render( 'AcmeAuditBundle:AuditFormField:edit.html.twig', array(
            'field'     => $field,
            'form'      => $form->createView(),
        ));
    }  
... 
}

FormFieldType.php

<?php

namespace Acme\AuditBundle\Form\Type;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;
use Acme\AuditBundle\Entity\AuditScore;
use Acme\AuditBundle\Entity\AuditFormField;

class AuditFormFieldType extends AbstractType
{
...

    public function buildForm( FormBuilderInterface $builder, array $options )
    {
        ...
        $builder->add( 'section', 'audit_section', array(
            'data' => ( isset($options['section']) ) ? $options['section']->getId() : null,
        ));
        ...
    }
...

    public function setDefaultOptions( OptionsResolverInterface $resolver )
    {
        $resolver->setDefaults( array(
            'data_class' => 'Acme\AuditBundle\Entity\AuditFormField',
            'section'    => null,
        ));
    }
}

SectionType.php

<?php

namespace Acme\AuditBundle\Form\Type;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\Extension\Core\ChoiceList\SimpleChoiceList;
use Symfony\Component\OptionsResolver\Options;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;
use Doctrine\Common\Persistence\ObjectManager;

class SectionType extends AbstractType
{
    private $repository;

    public function __construct( ObjectManager $objectManager )
    {
        $this->repository = $objectManager->getRepository( 'AcmeAuditBundle:AuditFormSection' );
    }

    public function setDefaultOptions( OptionsResolverInterface $resolver )
    {
        $type = $this;
        $choiceList = function( Options $options ) use ( $type )
        {
            return new SimpleChoiceList( $type->getSections( $options['auditform']) );
        };

        $resolver->setDefaults( array(
            'choice_list'   => $choiceList,
            'virtual'       => true,
            'empty_value'   => '(Select Section)',
            'empty_data'    => null,
            'auditform'     => null,
        ));
    }

    public function getSections( $auditform = null )
    {
        $array = array();

        foreach( $this->repository->getSections( $auditform ) as $set )
        {
            if( !$set->getAuditForm() ) { continue; }
            if( !array_key_exists( $set->getAuditForm()->getTitle(), $array ))
            {
                $array[$set->getAuditForm()->getTitle()] = array();
            }
            $array[$set->getAuditForm()->getTitle()][$set->getId()] = $set;
        }

        return $array;
    }

    public function getParent()
    {
        return 'choice';
    }

    public function getName()
    {
        return 'audit_section';
    }
}