How can I link a user with a shopping cart?

My app has both users and a shopping cart.

Theres currently no link between users and shopping carts.

At the moment regardless of if a user is logged in or not there is only one shopping cart available, the current_cart is created when a product is added and an order_transaction is created when the cart is paid for (success or fail). If successful, a new cart will be created the next time a product is added to the cart.

How can I link a cart with a user, so each user has a new cart created for them when adding a product?

application_controller

  def current_user
    @current_user ||= User.find(session[:user_id]) if session[:user_id]
  end

  def current_cart
    if session[:cart_id]
      @current_cart ||= Cart.find(session[:cart_id])
      session[:cart_id] = nil if @current_cart.purchased_at
    end
    if session[:cart_id].nil?
      @current_cart = Cart.create!
      session[:cart_id] = @current_cart.id
    end
    @current_cart
  end

routes

  get "log_in" => "sessions#new", :as => "log_in"
  get "log_out" => "sessions#destroy", :as => "log_out"
  get "sign_up" => "users#new", :as => "sign_up"

  get "cart" => "carts#show", :as => "current_cart"

  resources :orders
  resources :line_items
  resources :carts    
  resources :products
  resources :order_transactions

  resou开发者_运维问答rces :sessions
  resources :users

line_items_controller

class LineItemsController < ApplicationController
  def create
    @product = Product.find(params[:product_id])
    @line_item = LineItem.create!(:cart => current_cart, :product => @product, :quantity => 1, :unit_price => @product.price)
    flash[:notice] = "Added #{@product.name} to cart."
    redirect_to current_cart_url
  end
end

Thanks for any help its much appreciated!

The easiest way to do this is to make the user have a cart

class User < ActiveRecord::Base
  has_one :cart

  def current_cart
    if self.cart.empty?
      self.cart.create!
    end
    self.cart
  end
end

class Cart < ActiveRecord::Base
  belongs_to :user

  def add_line_item(item)
    etc...
  end
end

class ApplicationController < ActionController::Base
  def current_user
    @current_user ||= User.find(session[:user_id]) if session[:user_id]
  end

  def current_cart
    current_user.current_cart if current_user.present?
  end
end

I would recommend this. That way, you only have ONE thing to keep track of in session. You should also try to move as much of the "business logic" DOWN to the model tier, to make it easier to test.