Doctrine\ODM\MongoDB\Persisters\DocumentPersister::update PHP Method

    public function update($document, array $options = array())
    {
        $id = $this->uow->getDocumentIdentifier($document);
        $update = $this->dp->prepareUpdateData($document);

        if ( ! empty($update)) {

            $id = $this->class->getDatabaseIdentifierValue($id);
            $query = array('_id' => $id);

            // Include versioning updates
            if ($this->class->isVersioned) {
                $versionMapping = $this->class->fieldMappings[$this->class->versionField];
                $currentVersion = $this->class->getFieldValue($document, $this->class->versionField);
                if ($versionMapping['type'] === 'int') {
                    $nextVersion = $currentVersion + 1;
                    $update[$this->cmd . 'inc'][$versionMapping['name']] = 1;
                    $query[$versionMapping['name']] = $currentVersion;
                    $this->class->setFieldValue($document, $this->class->versionField, $nextVersion);
                } elseif ($versionMapping['type'] === 'date') {
                    $nextVersion = new \DateTime();
                    $update[$this->cmd . 'set'][$versionMapping['name']] = new \MongoDate($nextVersion->getTimestamp());
                    $query[$versionMapping['name']] = new \MongoDate($currentVersion->getTimestamp());
                    $this->class->setFieldValue($document, $this->class->versionField, $nextVersion);
                }
                $options['safe'] = true;
            }

            if ($this->class->isLockable) {
                $isLocked = $this->class->getFieldValue($document, $this->class->lockField);
                $lockMapping = $this->class->fieldMappings[$this->class->lockField];
                if ($isLocked) {
                    $update[$this->cmd . 'unset'] = array($lockMapping['name'] => true);
                } else {
                    $query[$lockMapping['name']] = array($this->cmd . 'exists' => false);
                }
            }

            if ($this->dm->getEventManager()->hasListeners(Events::onUpdatePrepared)) {
                $this->dm->getEventManager()->dispatchEvent(
                    Events::onUpdatePrepared, new OnUpdatePreparedArgs($this->dm, $document, $update)
                );
            }

            $result = $this->collection->update($query, $update, $options);

            if (($this->class->isVersioned || $this->class->isLockable) && ! $result['n']) {
                throw LockException::lockFailed($document);
            }
        }
    }