skeeks\cms\models\CmsContentElementFile::rules PHP Method

    public function rules()
    {
        return [[['created_by', 'updated_by', 'created_at', 'updated_at', 'storage_file_id', 'content_element_id', 'priority'], 'integer'], [['storage_file_id', 'content_element_id'], 'required'], [['storage_file_id', 'content_element_id'], 'unique', 'targetAttribute' => ['storage_file_id', 'content_element_id'], 'message' => \Yii::t('skeeks/cms', 'The combination of Storage File ID and Content Element ID has already been taken.')]];
    }