function validate($entity)
{
$errors = parent::validate($entity);
# Detect and prevent loop creation
$node_id = $entity['parent_id'];
while ($entity['id'] && $node_id) {
if ($node_id == $entity['id']) {
$errors['parent_id'] = lang('Invalid parent activity');
break;
}
$next = $this->read_single($node_id);
$node_id = $next['parent_id'];
}
return $errors;
}