#routes.rb

   resources :topics do | topic |
     resources :notes
   end

#controller

  def new
    @topic = Topic.first(:id => params[:topic.id])
    @note = Note.new
    render @note
  end


#view

%h1
  New Note :

%p
  =form_for(@note, :action => resource(@topic,:notes)) do
    %p
      = text_field :title, :label => "Title"
    %p
      Note Details
      %br/
      =text_area :body, :rows => 15, :cols => 60
    %p
      = submit "Create"
%p
  = link_to 'Back', resource(@topic)