fields_for.rb

# MODELS:
class Stencil < ActiveRecord::Base
  has_one :stencil_config, :dependent => :destroy
  accepts_nested_attributes_for :stencil_config
end

class StencilConfig < ActiveRecord::Base
  belongs_to :stencil
end


# CONTROLLERS:
class Admin::StencilsController < ApplicationController
  # GET /admin/stencils/new
  def new
    @stencil = Stencil.new
    @stencil.build_stencil_config
  end
end


class Admin::StencilConfigsController < ApplicationController
  # GET /admin/stencil_configs/new
  def new
    @stencil_config = StencilConfig.new
  end
end

#VIEW _FORM (trimmed):
<%= form_for([:admin, @stencil]) do |f| %>
  
  <div class="field">
    <%= f.label :client %><br />
    <%=   f.select(:client_id, Client.find(:all).collect {|c| [ c.name, c.id ] }) %>
  </div>

  <% f.fields_for :stencil_config do |stencil_config| %>
   asd asd 
    <div class="field">
      <%= stencil_config.label :title %><br />
      <%= stencil_config.text_field :title %>
    </div>

    <div class="field">
      <%= stencil_config.label :description %><br />
      <%= stencil_config.text_area :description %>
    </div>
  <% end %>

<% end %>