Explicitly set Id with Doctrine when using "AUTO" strategy

Although your solution work fine with MySQL, I failed to make it work with PostgreSQL as It's sequence based.

I've to add this line to make it work perfectly :

$metadata->setIdGenerator(new \Doctrine\ORM\Id\AssignedGenerator());

Perhaps what doctrine changed but now right way is:

$metadata->setIdGeneratorType(\Doctrine\ORM\Mapping\ClassMetadata::GENERATOR_TYPE_NONE);

In case the entity is part of a class table inheritance you need to change the id-generator in the class metadata for both entities (the entity you are persisting and the root entity)

New solution works fine only when ALL entities have id before insert. When one entity has ID and another one does not - new solution is failing.

I use this function for import all my data:

function createEntity(\Doctrine\ORM\EntityManager $em, $entity, $id = null)
{
    $className = get_class($entity);
    if ($id) {
        $idRef = new \ReflectionProperty($className, "id");
        $idRef->setAccessible(true);
        $idRef->setValue($entity, $id);

        $metadata = $em->getClassMetadata($className);
        /** @var \Doctrine\ORM\Mapping\ClassMetadataInfo $metadata */
        $generator = $metadata->idGenerator;
        $generatorType = $metadata->generatorType;

        $metadata->setIdGenerator(new \Doctrine\ORM\Id\AssignedGenerator());
        $metadata->setIdGeneratorType(\Doctrine\ORM\Mapping\ClassMetadata::GENERATOR_TYPE_NONE);

        $unitOfWork = $em->getUnitOfWork();
        $persistersRef = new \ReflectionProperty($unitOfWork, "persisters");
        $persistersRef->setAccessible(true);
        $persisters = $persistersRef->getValue($unitOfWork);
        unset($persisters[$className]);
        $persistersRef->setValue($unitOfWork, $persisters);

        $em->persist($entity);
        $em->flush();

        $idRef->setAccessible(false);
        $metadata->setIdGenerator($generator);
        $metadata->setIdGeneratorType($generatorType);

        $persisters = $persistersRef->getValue($unitOfWork);
        unset($persisters[$className]);
        $persistersRef->setValue($unitOfWork, $persisters);
        $persistersRef->setAccessible(false);
    } else {
        $em->persist($entity);
        $em->flush();
    }
}