Grouped Select Box for Polymorphic Associations

_form.html.erb

<%= form_for(@promotion, :html => { :multipart => true }) do |f| %>
 
  <%= select_tag 'owner', grouped_owners_for_select %>

<% end %>

promotions_controller.rb

class Admin::PromotionsController < AdminController

  before_filter :set_owner, :only => [:create, :update]

  private

    def set_owner
      if owner = params[:owner]
        params[:promotion][:owner_id], params[:promotion][:owner_type] = owner.split('-')
      end
    end

end

promotions_helper.rb

module Admin::PromotionsHelper

  def grouped_owners_for_select
    grouped_options = {
      'Products' => Product.all.map(&owner_option_for_select),
      'Pages' => Page.all.map(&owner_option_for_select)
    }
    grouped_options_for_select(grouped_options, "#{@promotion.owner_id}-#{@promotion.owner_type}")
  end

  def owner_option_for_select
    lambda {|record| [record.title, "#{record.id}-#{record.class.name}"] }
  end

end