public function getIdentifierValues($entity)
    {
        if ($this->isIdentifierComposite) {
            $id = array();

            foreach ($this->identifier as $idField) {
                $value = $this->reflFields[$idField]->getValue($entity);

                if ($value !== null) {
                    $id[$idField] = $value;
                }
            }

            return $id;
        }

        $id = $this->identifier[0];
        $value = $this->reflFields[$id]->getValue($entity);

        if (null === $value) {
            return array();
        }

        return array($id => $value);
    }