Subscription::setUserId PHP Method

    function setUserId($userId)
    {
        return $this->setData('userId', $userId);
    }

 /**
  * Subscribe $user to a given $object
  *
  * @param User $user
  * @param ProjectObject $object
  * @return boolean
  */
 function subscribe($user, $object)
 {
     if (!$object->can_have_subscribers) {
         return new InvalidParamError('$object', $object, '$object does not support subscribers', true);
     }
     // if
     if (Subscriptions::isSubscribed($user, $object, false)) {
         return true;
     }
     // if
     $subscription = new Subscription();
     $subscription->setUserId($user->getId());
     $subscription->setParentId($object->getId());
     $save = $subscription->save();
     if ($save && !is_error($save)) {
         Subscriptions::dropUserCache($user);
         return true;
     }
     // if
     return $save;
 }