Doctrine\ODM\MongoDB\UnitOfWork::scheduleOrphanRemoval PHP Method

    public function scheduleOrphanRemoval($document)
    {
        $this->orphanRemovals[spl_object_hash($document)] = $document;
    }

 /**
  * {@inheritdoc}
  */
 public function clear()
 {
     if ($this->initialized && $this->isEmpty()) {
         return;
     }
     if ($this->isOrphanRemovalEnabled()) {
         $this->initialize();
         foreach ($this->coll as $element) {
             $this->uow->scheduleOrphanRemoval($element);
         }
     }
     $this->mongoData = array();
     $this->coll->clear();
     // Nothing to do for inverse-side collections
     if (!$this->mapping['isOwningSide']) {
         return;
     }
     // Nothing to do if the collection was initialized but contained no data
     if ($this->initialized && empty($this->snapshot)) {
         return;
     }
     $this->changed();
     $this->uow->scheduleCollectionDeletion($this);
     $this->takeSnapshot();
 }