public function getTimestampField()
    {
        if ($this->timestamp_field === null) {
            $fields = $this->pool->getTypeFields($this->getRegisteredType());

            if (in_array('updated_at', $fields)) {
                $this->timestamp_field = 'updated_at';
            } elseif (in_array('created_at', $fields)) {
                $this->timestamp_field = 'created_at';
            } else {
                $this->timestamp_field = false;
            }
        }

        return $this->timestamp_field;
    }