private function setMultiValueRelationship($key, $foreign_entities)
{
$this->getDriver()->clearMultiValueIndex($key);
if ($foreign_entities) {
$values = [];
foreach ($foreign_entities as $entity) {
$rel_metadata = $this->getMapper()->getEntityMetadata($entity);
$rel_reader = new Reader($rel_metadata, $entity);
$values[] = $rel_reader->getId();
}
$this->getDriver()->addMultiValueIndex($key, $values);
}
}