src/Service/queryService.php
public function fetchField($doName, $searchRule, $fieldName)
    {
        $rec = $this->fetchRecord($doName, $searchRule);
        if ($rec)
            return $rec[$fieldName];
        return null;
    }
public function fetchField($doName, $searchRule, $fieldName)
    {
        $rec = $this->fetchRecord($doName, $searchRule);
        if ($rec)
            return $rec[$fieldName];
        return null;
    }
Fetch field

@param string $doName data object name
@param string $searchRule search rule
@param string $fieldName field name
@return mixed