public function actionAddSynonyms($class, $headword, $word, $addMissing = true)
    {
        $extMgr = Yii::$app->rhoone->ext;
        /* @var $extMgr \rhoone\base\ExtensionManager */
        $model = $extMgr->getModel($class);
        $headwordModel = $model->getHeadwords()->andWhere(['word' => $headword])->one();
        if (!$headwordModel) {
            if ($addMissing) {
                $headwordModel = $model->setHeadword(new Headword(['word' => $headword]));
            } else {
                throw new Exception("The headword: `" . $headword . "` does not exist.");
            }
        }
        try {
            if (!$headwordModel->setSynonyms($word)) {
                throw new Exception("Failed to add synonyms: `" . $word . "`");
            }
        } catch (\Exception $ex) {
            throw new Exception($ex->getMessage());
        }
        echo "The synonyms `" . $word . "` is added to `" . $class . "`";
        return 0;
    }