caching in Rails 4 book Agile Web Development with Rails 4

gistfile1.rb

# in development.rb
config.action_controller.perform_caching = true

# in app/models/product.rb
def self.latest
  Product.order(:updated_at).last
end

# in app/views/store/index.html.erb  
<% cache [ 'store', Product.latest ] do %>
  <% @products.each do |product| %>
    <% cache [ 'entry',  product ] do %>
      <div class="entry">
        <%= image_tag(product.image_url) %>
        <h3><%= product.title %></h3>
        <%= sanitize(product.description) %>
        <div class="price_line">
          <span class="price"><%= number_to_currency(product.price) %></span>
        </div>
      </div>
    <% end %>
  <% end %>
<% end %>