/**
  * {@inheritdoc}
  */
 public function slice(PersistentCollection $collection, $offset, $length = null)
 {
     return $this->persister->slice($collection, $offset, $length);
 }
 /**
  * {@inheritDoc}
  */
 public function loadCriteria(PersistentCollection $collection, Criteria $criteria)
 {
     return $this->persister->loadCriteria($collection, $criteria);
 }