function on_delete($post_master)
{
// if tag is not related to any other group, delete it
$list = new TagsToTagsGroups_list();
//check if tag is related to any other group, if not remove it
if (!$list->search(array('search_tag_id' => $this->tag_id, 'search_not_id' => $this->id))) {
//delete directly to avoid calling on_delete actions recursively
$post_master->sql_delete_list('articles_tags', "tag_id={$this->tag_id}");
$post_master->sql_delete_list('tags', "id={$this->tag_id}");
}
}
