Iteration G2.

app/controllers/products_controller.rb

@@ -65,6 +65,16 @@ class ProductsController < ApplicationController
     end
   end
 
+  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
+
   private
     # Use callbacks to share common setup or constraints between actions.
     def set_product

app/models/product.rb

@@ -1,5 +1,6 @@
 class Product < ApplicationRecord
   has_many :line_items
+  has_many :orders, through: :line_items
 
   before_destroy :ensure_not_referenced_by_any_line_item
 

app/views/products/who_bought.atom.builder

@@ -0,0 +1,40 @@
+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

config/routes.rb

@@ -4,6 +4,9 @@ Rails.application.routes.draw do
   resources :carts
   root 'store#index', as: 'store_index'
 
-  resources :products
+  resources :products do
+    get :who_bought, on: :member
+  end
+
   # For details on the DSL available within this file, see http://guides.rubyonrails.org/routing.html
 end