Workaround for https://github.com/ramsey/uuid-doctrine/issues/16

dic.xml

<service id="umpirsky.form.type.uuid_entity_type" class="Umpirsky\Form\Type\UuidEntityType">
    <argument type="service" id="doctrine" />
    <tag name="form.type" />
</service>

ORMUuidQueryBuilderLoader.php

<?php

namespace Umpirsky\Form\ChoiceList;

use Doctrine\ORM\QueryBuilder;
use Doctrine\DBAL\Connection;
use Doctrine\DBAL\Types\Type;
use Doctrine\DBAL\Platforms\AbstractPlatform;
use Symfony\Bridge\Doctrine\Form\ChoiceList\EntityLoaderInterface;
use Symfony\Component\Form\Exception\LogicException;

class ORMUuidQueryBuilderLoader implements EntityLoaderInterface
{
    private $queryBuilder;
    private $platform;

    public function __construct(QueryBuilder $queryBuilder, AbstractPlatform $platform)
    {
        $this->queryBuilder = $queryBuilder;
        $this->platform = $platform;
    }

    /**
     * {@inheritdoc}
     */
    public function getEntities()
    {
        return $this->queryBuilder->getQuery()->execute();
    }

    /**
     * {@inheritdoc}
     */
    public function getEntitiesByIds($identifier, array $values)
    {
        $qb = clone $this->queryBuilder;
        $alias = current($qb->getRootAliases());
        $parameter = 'ORMUuidQueryBuilderLoader_getEntitiesByIds_'.$identifier;
        $parameter = str_replace('.', '_', $parameter);
        $where = $qb->expr()->in($alias.'.'.$identifier, ':'.$parameter);

        // Guess type
        $entity = current($qb->getRootEntities());
        $metadata = $qb->getEntityManager()->getClassMetadata($entity);
        if ('uuid_binary_ordered_time' !== $metadata->getTypeOfField($identifier)) {
            throw new LogicException(sprintf(
                'ORMUuidQueryBuilderLoader supports uuid_binary_ordered_time identifiers only, %s given.',
                $metadata->getTypeOfField($identifier)
            ));
        }

        $parameterType = Connection::PARAM_STR_ARRAY;

        $values = array_map(function ($value) {
            return Type::getType('uuid_binary_ordered_time')->convertToDatabaseValue($value, $this->platform);
        }, array_values(array_filter($values, function ($v) {
            return '' !== (string) $v;
        })));

        if (!$values) {
            return [];
        }

        return $qb->andWhere($where)
            ->getQuery()
            ->setParameter($parameter, $values, $parameterType)
            ->getResult()
        ;
    }
}

UuidEntityType.php

<?php

namespace Umpirsky\Form\Type;

use Umpirsky\Form\ChoiceList\ORMUuidQueryBuilderLoader;
use Doctrine\Common\Persistence\ObjectManager;
use Symfony\Bridge\Doctrine\Form\Type\EntityType;

class UuidEntityType extends EntityType
{
    public function getLoader(ObjectManager $manager, $queryBuilder, $class)
    {
        return new ORMUuidQueryBuilderLoader($queryBuilder, $manager->getConnection()->getDatabasePlatform());
    }
}