/**
  * Return the relation ID for the given blog ID and term taxonomy ID.
  *
  * @param int $site_id          Blog ID.
  * @param int $term_taxonomy_id Term taxonomy ID.
  *
  * @return string
  */
 public function get_relation_id($site_id, $term_taxonomy_id)
 {
     $translation_ids = $this->content_relations->get_existing_translation_ids($site_id, 0, $term_taxonomy_id, 0, 'term');
     if (!$translation_ids) {
         return '';
     }
     $relation = reset($translation_ids);
     return $relation['ml_source_blogid'] . '-' . $relation['ml_source_elementid'];
 }