Agile Web Development with Rails, Edition 4

11.2 Iteration F2: Creating an AJAX-Based Cart 10.4 Playtime

11.1 Iteration F1: Moving the Cart

Refactor the cart view into partials, and reference the result from the layout.

Create a "partial" view, for just one line item

edit app/views/line_items/_line_item.html.erb

<tr>

  <td><%= line_item.quantity %>&times;</td>

  <td><%= line_item.product.title %></td>

  <td class="item_price"><%= number_to_currency(line_item.total_price) %></td>

</tr>

Replace that portion of the view with a callout to the partial

edit app/views/carts/show.html.erb

<% if notice %>

<p id="notice"><%= notice %></p>

<% end %>

<div class="cart_title">Your Cart</div>

<table>

  <%= render(@cart.line_items) %>

  <tr class="total_line">

    <td colspan="2">Total</td>

    <td class="total_cell"><%= number_to_currency(@cart.total_price) %></td>

  </tr>

</table>

<%= button_to 'Empty cart', @cart, method: :delete,

    confirm: 'Are you sure?' %>

Make a copy as a partial for the cart controller

cp app/views/carts/show.html.erb app/views/carts/_cart.html.erb

Modify the copy to reference the (sub)partial and take input from @cart

edit app/views/carts/_cart.html.erb

<div class="cart_title">Your Cart</div>

<table>

  <%= render(cart.line_items) %>

  <tr class="total_line">

    <td colspan="2">Total</td>

    <td class="total_cell"><%= number_to_currency(cart.total_price) %></td>

  </tr>

</table>

<%= button_to 'Empty cart', cart, method: :delete,

    confirm: 'Are you sure?' %>

Keep things DRY

edit app/views/carts/show.html.erb

<% if notice %>

<p id="notice"><%= notice %></p>

<% end %>

<%= render @cart %>

Reference the partial from the layout.

edit app/views/layouts/application.html.erb

<!DOCTYPE html>

<html>

<head>

  <title>Pragprog Books Online Store</title>

  <%= stylesheet_link_tag "application" %>

  <%= javascript_include_tag "application" %>

  <%= csrf_meta_tag %>

</head>

<body class="<%= controller.controller_name %>">

  <div id="banner">

    <%= image_tag("logo.png") %>

    <%= @page_title || "Pragmatic Bookshelf" %>

  </div>

  <div id="columns">

    <div id="side">

      <div id="cart">

        <%= render @cart %>

      </div>

      <ul>

        <li><a href="http://www....">Home</a></li>

        <li><a href="http://www..../faq">Questions</a></li>

        <li><a href="http://www..../news">News</a></li>

        <li><a href="http://www..../contact">Contact</a></li>

      </ul>

    </div>

    <div id="main">

      <%= yield %>

    </div>

  </div>

</body>

</html>

Insert a call in the controller to find the cart

edit app/controllers/store_controller.rb

  def index

    @products = Product.order(:title)

    @cart = current_cart

end

Add a small bit of style.

edit app/assets/stylesheets/carts.css.scss

// Place all the styles related to the Carts controller here.

// They will automatically be included in application.css.

// You can use Sass (SCSS) here: http://sass-lang.com/

.carts, #side #cart {

  .cart_title {

    font: 120% bold;

  .item_price, .total_line {

    text-align: right;

  .total_line .total_cell {

    font-weight: bold;

    border-top: 1px solid #595;

edit app/assets/stylesheets/application.css.scss

  #side {

    float: left;

    padding: 1em 2em;

    width: 13em;

    background: #141;

    form, div {

      display: inline;

    input {

      font-size: small;

    #cart {

      font-size: smaller;

      color:     white;

      table {

        border-top:    1px dotted #595;

        border-bottom: 1px dotted #595;

        margin-bottom: 10px;

    ul {

      padding: 0;

      li {

        list-style: none;

a {

          color: #bfb;

          font-size: small;

Change the redirect to be back to the store.

edit app/controllers/line_items_controller.rb

  def create

    @cart = current_cart

    product = Product.find(params[:product_id])

    @line_item = @cart.add_product(product.id)

    respond_to do |format|

      if @line_item.save

        format.html { redirect_to store_url }

        format.json { render json: @line_item,

          status: :created, location: @line_item }

      else

        format.html { render action: "new" }

        format.json { render json: @line_item.errors,

          status: :unprocessable_entity }

end

end

end

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post /line_items?product_id=3

product_id => 3

You are being redirected.

get http://localhost:3000/