/**
  * Tells the DocumentManager to make an instance managed and persistent.
  *
  * The document will be entered into the database at or before transaction
  * commit or as a result of the flush operation.
  * 
  * NOTE: The persist operation always considers documents that are not yet known to
  * this DocumentManager as NEW. Do not pass detached documents to the persist operation.
  *
  * @param object $document The instance to make managed and persistent.
  */
 public function persist($document)
 {
     if (!is_object($document)) {
         throw new \InvalidArgumentException(gettype($document));
     }
     $this->_unitOfWork->persist($document);
 }