storing user_id in a form post

hey guys, got a simple question here new to rails and loving it!

i have form

<%= form_tag :action => "answer", :id => @question %>

   Body: <br/>
   <%= text_area "answer", "body" %><br/>

   <%= submit_tag 'Answer' %>
</form>

and in my controller

  def answer

Question.find(params[:id]).question_answers.create(params[:answer])
      redirect_to :action => "show", :id => params[:id]
   end

its storing the infromation (body, question_id) but not my user_id ,
how could i store it ?

Before I started writing my applications with a RESTful design, I
always passed stuff like that in a hidden field.

If you go the RESTful approach, you can configure it so that the
user_id will always be part of the request url.

If you have no idea what I mean by RESTful, then I will post back with
some links to get you going. Let me know.