validating a form with a foreign key

Hi there.
I have a problem with validating a form, where is foreign key present.
I have a table like this:
  id
  name
  password
  status_id

This is the way that status_id is implemented to the users table.
<td><%= select_tag ('status_id', options_for_select([['-- choose one
--', nil]] + @status.collect { |stat| [stat.status, stat.id]},
@user.status_id))%></td>