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

However, iteliminates the possibility of high availability (sessions cannot be shared
between two servers unless they communicate), and a server that is restarted typi-
cally loses its sessions (unless storing them in persistent storage, which negates many
advantages of sticky sessions). Neither of these options is terribly RESTful, and so we
promote statelessness as far as is practical.

Resourceful session state: An example

So what is the RESTful alternative to holding session state on the server? As with
nearly any problem REST developers face, the solution is tomodel it as a resource.
With the exception of authentication information (discussed later in the chapter),
nearly anything that would be stored in a session could also be factored into a
resource.

Consider the example of a shopping cart. A typical, simple, non-RESTful Rails
implementation would look something like this:

app/models/cart.rb

A simple Hash that defaults to zero.

Used to map product IDs to quantities to represent a shopping cart.

class Cart < Hash
def initialize
super(0)
end
end

app/controllers/carts_controller.rb
class CartsController < ApplicationController
before_filter :set_cart

def add_product

product_id = params[:id]

quantity = params[:quantity] || 1

# Increment cart quantity by provided quantity

session[:cart][product_id.to_i] += quantity.to_i

end

def update_quantity

product_id = params[:id]

quantity = params[:quantity]

# Set cart quantity to provided quantity

session[:cart][product_id.to_i] = quantity.to_i

end

def remove_product

product_id = params[:id]