public function removeUserId($userId)
{
if (!$userId || !self::hasUserId($userId)) {
return;
}
for ($i = 1; $i <= 5; $i++) {
$field = "user_id{$i}";
if ($this->{$field} && $this->{$field} == $userId) {
$this->{$field} = null;
}
}
}