Simple Entity Form Type

IdentityToEntityTransformer.php

<?php
use Symfony\Component\Form\DataTransformerInterface;
use Symfony\Component\Form\Exception\TransformationFailedException;

class IdentityToEntityTransformer implements DataTransformerInterface
{
    private $repository;
    private $repositoryMethod;
    private $identifierMethod;

    /**
     * @param object $repository
     * @param string $repositoryMethod
     * @param string $identifierMethod
     */
    public function __construct($repository, $repositoryMethod, $identifierMethod)
    {
        $this->repository = $repository;
        $this->repositoryMethod = $repositoryMethod;
        $this->identifierMethod = $identifierMethod;
    }

    /**
     * @param object $entity
     * @return string
     */
    public function transform($entity)
    {
        if (!$entity) {
            return;
        }

        return (string) call_user_func([$entity, $this->identifierMethod]);
    }

    /**
     * @param mixed $id
     * @return null|object|void
     */
    public function reverseTransform($id)
    {
        if (null !== $id && !is_scalar($id)) {
            throw new TransformationFailedException('Expected a scalar.');
        }

        if ('' === $id || null === $id) {
            return;
        }

        $entity = call_user_func([$this->repository, $this->repositoryMethod], $id);

        if (!$entity) {
            throw new TransformationFailedException(sprintf('The entity identified by "%s" does not exist', $id));
        }

        return $entity;
    }
}

SimpleEntityType.php

<?php

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;

class SimpleEntityType extends AbstractType
{
    /**
     * @param FormBuilderInterface $builder
     * @param array $options
     */
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder->addViewTransformer(new IdentityToEntityTransformer(
            $options['repository'],
            $options['repositoryMethod'],
            $options['identifierMethod']
        ));
    }

    /**
     * @param OptionsResolverInterface $resolver
     */
    public function setDefaultOptions(OptionsResolverInterface $resolver)
    {
        $resolver->setDefaults([
            'compound' => false,
            'repository' => null,
            'identifierMethod' => 'getId',
            'repositoryMethod' => 'get'
        ]);

        $resolver->setRequired(['repository']);
    }

    /**
     * @return string
     */
    public function getName()
    {
        return 'simple_entity';
    }
}