private function get_tags()
{
if ($this->tags_object == null) {
$result = Tags::vocabulary()->get_associations($this->id);
if ($result) {
$tags = new Terms($result);
} else {
$tags = new Terms();
}
$this->tags_object = $tags;
} else {
$tags = $this->tags_object;
}
return $tags;
}