protected function processDeletes() {
    $deletedOids = [];
    $deleteOids = array_keys($this->deletedObjects);
    while (sizeof($deleteOids) > 0) {
      $key = array_shift($deleteOids);
      if (self::$isDebugEnabled) {
        self::$logger->debug("Process delete on object: ".$key);
      }
      $object = $this->deletedObjects[$key];
      $object->getMapper()->delete($object);
      unset($this->deletedObjects[$key]);
      $deletedOids[] = $key;
      $deleteOids = array_keys($this->deletedObjects);
    }
    return $deletedOids;
  }