XML seems to be increasingly de-emphasized these days, but here is the essence of what was in that section:

edit app/controllers/products_controller.rb def who_bought @product = Product.find(params[:id]) @latest_order = @product.orders.order(:updated_at).last if stale?(@latest_order) respond_to do |format| format.atom end end end Define an Atom view (using the Atom builder) edit app/views/products/who_bought.atom.builder atom_feed do |feed| feed.title "Who bought #{@product.title}" feed.updated @latest_order.try(:updated_at) @product.orders.each do |order| feed.entry(order) do |entry| entry.title "Order #{order.id}" entry.summary type: 'xhtml' do |xhtml| xhtml.p "Shipped to #{order.address}" xhtml.table do xhtml.tr do xhtml.th 'Product' xhtml.th 'Quantity' xhtml.th 'Total Price' end order.line_items.each do |item| xhtml.tr do xhtml.td item.product.title xhtml.td item.quantity xhtml.td number_to_currency item.total_price end end xhtml.tr do xhtml.th 'total', colspan: 2 xhtml.th number_to_currency \ order.line_items.map(&:total_price).sum end end xhtml.p "Paid by #{order.pay_type}" end entry.author do |author| author.name order.name author.email order.email end end end end Add "orders" to the Product class edit app/models/product.rb class Product < ApplicationRecord has_many :line_items has_many :orders, through: :line_items #... end