Iteration E1.

app/controllers/line_items_controller.rb

@@ -29,7 +29,7 @@ class LineItemsController < ApplicationController
   # POST /line_items.json
   def create
     product = Product.find(params[:product_id])
-    @line_item = @cart.line_items.build(product: product)
+    @line_item = @cart.add_product(product)
 
     respond_to do |format|
       if @line_item.save

app/models/cart.rb

@@ -1,3 +1,13 @@
 class Cart < ApplicationRecord
   has_many :line_items, dependent: :destroy
+
+  def add_product(product)
+    current_item = line_items.find_by(product_id: product.id)
+    if current_item
+      current_item.quantity += 1
+    else
+      current_item = line_items.build(product_id: product.id)
+    end
+    current_item
+  end
 end

app/views/carts/show.html.erb

@@ -4,6 +4,6 @@
 
 <ul>
   <% @cart.line_items.each do |item| %>
-    <li><%= item.product.title %></li>
+    <li><%= item.quantity %> &times; <%= item.product.title %></li>
   <% end %>
 </ul>

db/migrate/20161116085812_add_quantity_to_line_items.rb

@@ -0,0 +1,5 @@
+class AddQuantityToLineItems < ActiveRecord::Migration[5.0]
+  def change
+    add_column :line_items, :quantity, :integer, default: 1
+  end
+end

db/migrate/20161116091835_combine_items_in_cart.rb

@@ -0,0 +1,30 @@
+class CombineItemsInCart < ActiveRecord::Migration[5.0]
+  def up
+    Cart.all.each do |cart|
+      sums = cart.line_items.group(:product_id).sum(:quantity)
+
+      sums.each do |product_id, quantity|
+        if quantity > 1
+          cart.line_items.where(product_id: product_id).delete_all
+
+          item = cart.line_items.build(product_id: product_id)
+          item.quantity = quantity
+          item.save!
+        end
+      end
+    end
+  end
+
+  def down
+    LineItem.where('quantity > 1').each do |li|
+      li.quantity.times do
+        # item = Cart.find_by(:cart_id li.cart_id).line_items.build(product_id: li.product_id)
+        # item.save!
+        LineItem.create(cart_id: li.cart_id,
+                        product_id: li.product_id,
+                        quantity: 1)
+      end
+      li.destroy
+    end
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20161115211138) do
+ActiveRecord::Schema.define(version: 20161116091835) do
 
   create_table "carts", force: :cascade do |t|
     t.datetime "created_at", null: false
@@ -20,8 +20,9 @@ ActiveRecord::Schema.define(version: 20161115211138) do
   create_table "line_items", force: :cascade do |t|
     t.integer  "product_id"
     t.integer  "cart_id"
-    t.datetime "created_at", null: false
-    t.datetime "updated_at", null: false
+    t.datetime "created_at",             null: false
+    t.datetime "updated_at",             null: false
+    t.integer  "quantity",   default: 1
     t.index ["cart_id"], name: "index_line_items_on_cart_id"
     t.index ["product_id"], name: "index_line_items_on_product_id"
   end

test/controllers/line_items_controller_test.rb

@@ -23,7 +23,7 @@ class LineItemsControllerTest < ActionDispatch::IntegrationTest
     follow_redirect!
 
     assert_select 'h2', 'Your Pragmatic Cart'
-    assert_select 'li', 'Programming Ruby 1.9'
+    assert_select 'li', "1 \u00D7 Programming Ruby 1.9"
   end
 
   test "should show line_item" do