/**
     * Finds a document by its identifier.
     *
     * @param $id The identifier.
     * @param int $lockMode
     * @param int $lockVersion
     * @return object The document.
     */
    public function find($id, $lockMode = LockMode::NONE, $lockVersion = null)
    {
        // Check identity map first
        if ($document = $this->dm->getUnitOfWork()->tryGetById($id, $this->class->rootDocumentName)) {
            if ($lockMode != LockMode::NONE) {
                $this->dm->lock($document, $lockMode, $lockVersion);
            }

            return $document; // Hit!
        }

        $id = array('_id' => $id);

        if ($lockMode == LockMode::NONE) {
            return $this->dm->getUnitOfWork()->getDocumentPersister($this->documentName)->load($id);
        } else if ($lockMode == LockMode::OPTIMISTIC) {
            if (!$this->class->isVersioned) {
                throw LockException::notVersioned($this->documentName);
            }
            $document = $this->dm->getUnitOfWork()->getDocumentPersister($this->documentName)->load($id);

            $this->dm->getUnitOfWork()->lock($document, $lockMode, $lockVersion);

            return $document;
        } else {
            return $this->dm->getUnitOfWork()->getDocumentPersister($this->documentName)->load($id, null, array(), $lockMode);
        }
    }