TYPO3 Solr userFunc IndexQueue

IndexUserFunc.php

<?php
namespace Vendor\Extension\Solr\UserFunc;


class IndexUserFunc
{
    /**
     * This value is automatically inserted by userFunc handling
     * @var \TYPO3\CMS\Frontend\ContentObject\ContentObjectRenderer
     */
    public $cObj;

    /**
     * @param mixed $content
     * @param array $conf
     * @return string
     */
    public function doSomething($content, $conf) {
        /** @var \TYPO3\CMS\Core\Database\DatabaseConnection $db */
        $db = $GLOBALS['TYPO3_DB'];
        /** @var array $record */
        $record = $this->cObj->data;
        
        //$conf contains the configuration from typoscript index queue of this field. E.g. someParam

        $relatedRecord = $db->exec_SELECTgetSingleRow('title', 'mytable', 'local_uid = ' . $record['uid'] . ' AND foo = ' . $conf['someParam.']['myValue']);

        return $relatedRecord['title'];
    }
}

setup.ts

plugin.tx_solr.index.queue.myType = 1
plugin.tx_solr.index.queue.myType {
	table = tx_vendor_domain_model_product

	fields {
		title = title

		 # more fields

		myField_stringS = USER
    		myField_stringS.userFunc = Vendor\Extension\Solr\UserFunc\IndexUserFunc->doSomething
    		myField_stringS.someParam < lib.my.stuff

	}
}