202 | Chapter 7: REST, Resources, and Web Services

Let’s examine the routes that make this work:

config/routes.rb
map.resources :carts do |cart|
cart.resources :products, :controller => 'line_items'
end

Because we are conforming to the Rails conventions of how RESTful routes should
work, there is very little manual configuration here. We get a lot “for free,” just for
following the conventions:

• Incoming requests are mapped to the proper controller based not only on the
  URI but also on the HTT Pmethod used. (Some browsers and proxies do not
  support HTT Pmethods other thanGETandPOST; we will see later how Rails
  works around this.)


• We get named routes completely for free, including the ability to route to a spe-
  cific representation such as XML:
  carts_path # => /carts

cart_path(some_cart) # => /carts/123

formatted_cart_path(some_cart, :xml) # => /carts/123.xml

products_path(some_cart) # => /carts/123/products

product_path(some_cart, some_product) # => /carts/123/products/456

• The routing system pre-populates theparamshash with the ID variables we
  need, named appropriately. So, for a request to/carts/123/products/456, the
  paramshash will contain the pairs:cart_id => 123and:id => 456. We can use a
  before_filterin the controller to pick these off and retrieve them from the
  database, cleaning up the controller code.

Later in this chapter, we will explore the Rails RESTful routing system in detail. But
now, let’s take a look at the controllers that power the cart system. For simplicity, we
will ignore any responses that we might render in the real world, and instead focus
on sending correct HTT Presponse codes with no response body. (For this reason,
we have left out any kind of “view cart” action also.)

app/controllers/carts_controller.rb
class CartsController < ApplicationController

POST /carts

def create
@cart = Cart.create

Return 201 Created to indicate success; point to location of new cart

render :nothing => true, :status => :created, :location => cart_path(@cart)
end

# DELETE /carts/:id

def destroy

@cart = Cart.find(params[:id])

@cart.destroy

# Return 200 OK to indicate successful delete

render :nothing => true