public function getIdentifyingData()
    {
        $keys = array_keys($this->getEntityDescription()->getIdentifyingProperties());

        $data = array();

        foreach ($keys as $key) {
            if ($this->_data->isMaterialized($key)) {
                $value = $this->get($key);

                if ($value) {
                    $data[$key] = $value;
                }
            }
        }

        return $data;
    }