public function preparePlainTextValue($data, $entry_id = null, $truncate = false, $defaultValue = null)
 {
     if (!is_array($data) || is_array($data) && !isset($data['relation_id'])) {
         return parent::preparePlainTextValue($data, $entry_id, $truncate, $defaultValue);
     }
     if (!is_array($data['relation_id'])) {
         $data['relation_id'] = array($data['relation_id']);
     }
     $result = $this->findRelatedValues($data['relation_id']);
     $label = '';
     foreach ($result as $item) {
         $label .= strip_tags(htmlspecialchars_decode($item['value'])) . ', ';
     }
     return trim($label, ', ');
 }