building an order from a cart - ruby-on-rails

Question

i've been having issues trying to build a Cart + Cart/OrderItem + Order combination simple enough yet effective. I've looked around online but i couldn't find anything that fit, so i tried something but .. i'm a bit blocked atm, i don't see how to continue with this. The problem is that i don't know how to get the items in the order and start the cart from scratch (btw it's kind of messy). Also a nice simple tutorial on this would be appreciated as well. Do note i already went through agile web's book example, but for some reason i didn't follow it, it didn't seem to be what i was looking for.
controllers - cart + order
class CartsController < ApplicationController before_filter :initialize_cart
def add
#cart.add_item params[:id]
session["cart"] = #cart.serialize
product = Product.find(params[:id])
redirect_to :back, notice: "Added #{product.name} to cart." end
def show end
def checkout
#order = Order.new user: User.new end end
class OrdersController < ApplicationController
def index
#orders = Order.order('created_at desc').page(params[:page])
end
def show
end
def new
#order = Order.new
end
def create
#order = Order.new(order_params)
respond_to do |format|
if #order.save
format.html { redirect_to root_path, notice:
'Thank you for your order' }
format.json { render action: 'show', status: :created,
location: #order }
else
format.html { render action: 'new' }
format.json { render json: #order.errors,
status: :unprocessable_entity }
end
end
end
private
def set_order
#order = Order.find(params[:id])
end
def order_params
params.require(:order).permit(:pay_type, :user_id)
end
end
now the models
class Order < ActiveRecord::Base
belongs_to :user
PAYMENT_TYPES = [ "Check", "Credit card", "Purchase order" ]
validates :pay_type, inclusion: PAYMENT_TYPES
end
class CartItem
attr_reader :product_id, :quantity
def initialize product_id, quantity = 1
#product_id = product_id
#quantity = quantity
end
def product
Product.find product_id
end
def total_price
product.price * quantity
end
end
class Cart
attr_reader :items
def self.build_from_hash hash
items = if hash["cart"] then
hash["cart"]["items"].map do |item_data|
CartItem.new item_data["product_id"], item_data["quantity"]
end
else
[]
end
new items
end
def initialize items = []
#items = items
end
def add_item product_id
item = #items.find { |item| item.product_id == product_id }
if item
item+=1
else
#items << CartItem.new(product_id)
end
end
def empty?
#items.empty?
end
def count
#items.length
end
def serialize
items = #items.map do |item|
{
"product_id" => item.product_id,
"quantity" => item.quantity
}
end
{
"items" => items
}
end
def total_price
#items.inject(0) { |sum, item| sum + item.total_price }
end
end
Thank you.