Usando eventos preRemove/postRemove para obter quais consultas podem ser executadas e quais não podem

Acme\MyBundle\Entity\Car:
    type: entity
    table: cars
    id:
        id:
            type: integer
            id: true
            generator:
                strategy: AUTO
    fields:
        name:
            type: string
            length: '25'
            unique: true
        color:
            type: string
            length: '64'
    lifecycleCallbacks:
        preRemove: [entityDueToDeletion]
        postRemove: [entityDeleted]

class Car {

    // Getters & setters and so on, not going to copy them here for simplicity

    private static $preDeletedEntities;// static array that will contain entities due to deletion.
    private static $deletedEntities;// static array that will contain entities that were deleted (well, at least the SQL was thrown).

    public function entityDueToDeletion() {// This callback will be called on the preRemove event
        self::$preDeletedEntities[] = $this->getId();// This entity is due to be deleted though not deleted yet.
    }

    public function entityDeleted() {// This callback will be called in the postRemove event
        self::$deletedEntities[] = $this->getId();// The SQL to delete the entity has been issued. Could fail and trigger the rollback in which case the id doesn't get stored in the array.
    }

    public static function getDeletedEntities() {
        return array_slice(self::$preDeletedEntities, 0, count(self::$deletedEntities));
    }

    public static function getNotDeletedEntities() {
        return array_slice(self::$preDeletedEntities, count(self::$deletedEntities)+1, count(self::$preDeletedEntities));
    }

    public static function getFailedToDeleteEntity() {
        if(count(self::$preDeletedEntities) == count(self::$deletedEntities)) {
            return NULL; // Everything went ok
        }
        return self::$preDeletedEntities[count(self::$deletedEntities)]; // We return the id of the entity that failed.
    }

    public static function prepareArrays() {
        self::$preDeletedEntities = array();
        self::$deletedEntities = array();
    }
}

use Acme\MyBundle\Entity\Car;

$qb = $em->createQueryBuilder();
$ret = $qb
        ->select("c")
        ->from('AcmeMyBundle:Car', 'c')
        ->add('where', $qb->expr()->in('c.id', ':ids'))
        ->setParameter('ids', $arrayOfIds)
        ->getQuery()
        ->getResult();

Car::prepareArrays();// Initialize arrays (useful to reset them also)
foreach ($ret as $car) {// Second approach
    $em->remove($car);
}

try {
    $em->flush();
} catch (\Exception $e) {
    $couldBeDeleted = Car::getDeletedEntities();
    $entityThatFailed = Car::getFailedToDeleteEntity();
    $notDeletedCars = Car::getNotDeletedEntities();

    // Do what you please, you can delete those entities that didn't fail though you'll have to reset the entitymanager (it'll be closed by now due to the exception).

    return $this->render('AcmeMyBundle:Car:errors.html.twig', array(// I'm going to respond with the ids that could've succeded, the id that failed and those entities that we don't know whether they could've succeeded or not.
                'deletedCars' => $couldBeDeleted,
                'failToDeleteCar' => $entityThatFailed,
                'notDeletedCars' => $notDeletedCars,
    ));
}