1.0 4 张表

表1: products : name | price | active
表2: orders : subtotal | tax | shipping | total | order_status(references)
表3: order_items : product_id(references) | order_id(references) | unit_price | total_price | quantity
表4: order_status : name

2.0 表的关系

product <----belongs_to/has_many-----> order_item <----has_many/belongs_to-----> order

多对多关系一般不会用 has_and_belongs_to_many, 而是使用has_many :through 第三张表关联

order <-----belongs_to/has_many-----> order_status

models

1.0

rails g model Product name 'price:decimal{12,3}' active:boolean
rails g model OrderStatus name:string
rails g model Order 'subtotal:decimal{12,3}' 'tax:decimal{12,3}' 'shipping:decimal{12,3}' 'total:decimal{12,3}' order_status:references
rails g model OrderItem product:references order:references 'unit_price:decimal{12,3}' quantity:integer 'total_price:decimal{12,3}'
rake db:migrate

2.0

app/models/order.rb:

class Order < ActiveRecord::Base
  belongs_to :order_status
  has_many :order_items
  before_create :set_order_status
  before_save :update_subtotal

  def subtotal
    order_items.collect { |oi| oi.valid? ? (oi.quantity * oi.unit_price) : 0 }.sum
  end
private
  def set_order_status
    self.order_status_id = 1
  end

  def update_subtotal
    self[:subtotal] = subtotal
  end
end

app/models/order_item.rb:

class OrderItem < ActiveRecord::Base
  belongs_to :product
  belongs_to :order

  validates :quantity, presence: true, numericality: { only_integer: true, greater_than: 0 }
  validate :product_present
  validate :order_present

  before_save :finalize

  def unit_price
    if persisted?
      self[:unit_price]
    else
      product.price
    end
  end

  def total_price
    unit_price * quantity
  end

private
  def product_present
    if product.nil?
      errors.add(:product, "is not valid or is not active.")
    end
  end

  def order_present
    if order.nil?
      errors.add(:order, "is not a valid order.")
    end
  end

  def finalize
    self[:unit_price] = unit_price
    self[:total_price] = quantity * self[:unit_price]
  end
end

app/models/order_status.rb:

class OrderStatus < ActiveRecord::Base
  has_many :orders
end

app/models/product.rb:

class Product < ActiveRecord::Base
  has_many :order_items

  default_scope { where(active: true) }
end

controllers

rails g controller Products index
rails g controller Carts show
rails g controller OrderItems create update destroy

app/controllers/application_controller.rb:

class ApplicationController < ActionController::Base
  protect_from_forgery with: :exception
  helper_method :current_order

  def current_order
    if !session[:order_id].nil?
      Order.find(session[:order_id])
    else
      Order.new
    end
  end
end

app/controllers/carts_controller.rb:

class CartsController < ApplicationController
  def show
    @order_items = current_order.order_items
  end
end

app/controllers/order_items_controller.rb:

class OrderItemsController < ApplicationController
  def create
    @order = current_order
    @order_item = @order.order_items.new(order_item_params)
    @order.save
    session[:order_id] = @order.id
  end

  def update
    @order = current_order
    @order_item = @order.order_items.find(params[:id])
    @order_item.update_attributes(order_item_params)
    @order_items = @order.order_items
  end

  def destroy
    @order = current_order
    @order_item = @order.order_items.find(params[:id])
    @order_item.destroy
    @order_items = @order.order_items
  end
private
  def order_item_params
    params.require(:order_item).permit(:quantity, :product_id)
  end
end

app/controllers/products_controller.rb:

class ProductsController < ApplicationController
  def index
    @products = Product.all
    @order_item = current_order.order_items.new
  end
end

routes.rb:

Rails.application.routes.draw do
  resources :products, only: [:index]
  resource :cart, only: [:show]
  resources :order_items, only: [:create, :update, :destroy]
  root to: "products#index"
end