Rails nested photo file upload form

I have a class Scene, which has_one Photo, and Photo belongs_to Scene. I want to create a form that'll update or create Scene and Photo simultaneously - if Scene already exists, it'll update the Photo with scene_id Scene.id, otherwise, it'll make a new Scene and a new Photo, or if there's no new photo, it'll just update the one Scene field in question ("description").

However I don't have the slightest idea how. I get the feeling it looks nothing li开发者_运维问答ke these other forms.

Oh, and the Photo model is set up to use Attachment-fu.

In Scene Model

accepts_nested_attributes_for :photo

Form

<% form_for @scene do |scene_form| %>
  <!-- Fields for scene form -->

  <% scene_form.fields_for :photo do |photo_form| %>
    <!-- fields for photo form -->  
  <% end %>

<%= customer_form.submit %>
<% end %>