<% @products.each do |product| %>
<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, unit: '$') %></span>
  <%= button_to 'Add to Cart', line_items_path(product_id: product) %>
</div>
</div>
<% end %>

class LineItem < ActiveRecord::Base
  attr_accessible :cart_id, :product_id
  belongs_to :product
  belongs_to :cart
end

line_items_path(product)

line_items_path(product_id: product)

line_items_path(:product_id => product)

line_items_path({:product_id => product})