private function prepareClassConstants()
    {
        $descriptor = $this->getStorageDescriptor();
        $storage_name = $descriptor->getStorageName();

        if ($descriptor->hasField($storage_name . '_key')) {
            $fragment = new CNabuPHPConstantBuilder($this, 'INDEX_KEY', 'keys', 'string');
            $fragment->addComment("Index the list using the ${storage_name}_key field.");
            $this->addFragment($fragment);
        }

        if ($descriptor->hasField($descriptor->getStorageName() . '_order')) {
            $fragment = new CNabuPHPConstantBuilder($this, 'INDEX_ORDER', 'order', 'int');
            $fragment->addComment("Index the list using the ${storage_name}_order field.");
            $this->addFragment($fragment);
        }
    }