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

    public function getDocumentChangeSet($document)
    {
        $oid = spl_object_hash($document);
        if (isset($this->documentChangeSets[$oid])) {
            return $this->documentChangeSets[$oid];
        }
        return array();
    }

 /**
  * Prepares the update query to upsert a given document object in mongodb.
  *
  * @param object $document
  * @return array $updateData
  */
 public function prepareUpsertData($document)
 {
     $class = $this->dm->getClassMetadata(get_class($document));
     $changeset = $this->uow->getDocumentChangeSet($document);
     $updateData = array();
     foreach ($changeset as $fieldName => $change) {
         $mapping = $class->fieldMappings[$fieldName];
         /* Do nothing for embed-many or reference-many collections. If it
          * uses an atomic strategy, the data will be included when preparing
          * the atomic query in DocumentPersister::executeUpserts(). Other
          * strategies will be handled by CollectionPersister.
          */
         if ($mapping['type'] === ClassMetadata::MANY) {
             continue;
         }
         list($old, $new) = $change;
         // @Inc
         if ($mapping['type'] === 'increment') {
             if ($new >= $old) {
                 $updateData['$inc'][$mapping['name']] = $new - $old;
             } else {
                 $updateData['$inc'][$mapping['name']] = ($old - $new) * -1;
             }
             // @Field, @String, @Date, etc.
         } elseif (!isset($mapping['association'])) {
             if (isset($new) || $mapping['nullable'] === true) {
                 $updateData['$set'][$mapping['name']] = is_null($new) ? null : Type::getType($mapping['type'])->convertToDatabaseValue($new);
             }
             // @EmbedOne
         } elseif (isset($mapping['association']) && $mapping['association'] === ClassMetadata::EMBED_ONE) {
             // If we have a new embedded document then lets set the whole thing
             if ($new && $this->uow->isScheduledForInsert($new)) {
                 $updateData['$set'][$mapping['name']] = $this->prepareEmbeddedDocumentValue($mapping, $new);
                 // If we don't have a new value then do nothing on upsert
             } elseif (!$new) {
                 // Update existing embedded document
             } else {
                 $update = $this->prepareUpsertData($new);
                 foreach ($update as $cmd => $values) {
                     foreach ($values as $key => $value) {
                         $updateData[$cmd][$mapping['name'] . '.' . $key] = $value;
                     }
                 }
             }
             // @ReferenceOne
         } elseif (isset($mapping['association']) && $mapping['association'] === ClassMetadata::REFERENCE_ONE && $mapping['isOwningSide']) {
             if (isset($new) || $mapping['nullable'] === true) {
                 $updateData['$set'][$mapping['name']] = is_null($new) ? null : $this->prepareReferencedDocumentValue($mapping, $new);
             }
         }
         // @EmbedMany and @ReferenceMany are handled by CollectionPersister
     }
     // add discriminator if the class has one
     if (isset($class->discriminatorField)) {
         $updateData['$set'][$class->discriminatorField] = isset($class->discriminatorValue) ? $class->discriminatorValue : $class->name;
     }
     return $updateData;
 }