一本被人反复提及的书《哪儿来的天才》中说过，大部分所谓的天才都是通过反复的刻意练习得到的。当你的练习时间达到10000小时以后，你就会成为该领域的专家。

最近在学习rails如何实现RESTful Web Service。自己想给自己设计一个练习的模板，进行反复练习。开发过程采用的是TDD的方式进行开发。

练习背景：

我们涉及三个Domain对象，Products、Orders、Payment

1.新建工程rails-rest-practice

rails new rails-rest-practice

cd !$

bundle install

2.安装rspec-rails

在Gemfile中添加

gem "rspec-rails", :group => [:development, :test]

然后

bundle install

rails g rspec:install

在.rspec 中去掉 --warnings

3.GET /products => user get list of products

step 1：创建controller，返回HTTP Status 200

user products api如下：

GET   /products       user get list of products

创建文件：spec/products/products_controller_spec.rb

require ‘rails_helper‘

describe ProductsController, :type => :controller do
   describe ‘products controller‘ do
      it ‘get index of products‘ do
         get :index
         expect(response).to have_http_status(200)
      end
   end
end

have_http_status:http://rubydoc.info/gems/rspec-rails/RSpec/Rails/Matchers#have_http_status-instance_method

创建文件：app/controllers/products_controller.rb

class ProductsController < ApplicationController
   def index
   end
end

运行rake spec，得到错误：

     ActionController::UrlGenerationError:
       No route matches {:action=>"index", :controller=>"products"}

配置相关config/routes.rb

resources :products do
   collection do
      get :index
   end
end

运行rake spec，得到错误：

Failure/Error: get :index
     ActionView::MissingTemplate:

修改app/controllers/products_controller.rb

class ProductsController < ApplicationController
   def index
      render :nothing => true
   end
end

这样就完成我们的第一个步骤，虽然看似这个步骤什么都没测，其实不然，在这一步中，我们搭建好了routes，同时创建了必要的controller类和其对应的方法。

step 2:返回JSON

安装rabl

在Gemfile中添加rabl

gem ‘rabl‘

bundle install

参考Rails + rabl

修改测试：spec/products/products_controller_spec.rb

render_views

describe ‘products controller‘ do
   before(:all) do
      @products = [
         Product.new({:id => 1, :name => ‘apple juice‘, :description => ‘good‘}),
         Product.new({:id => 2, :name => ‘banana juice‘, :description => ‘just so so‘})
      ]
   end

   it ‘get index of products‘ do
      expect(Product).to receive(:all).and_return(@products).once

      get :index, {:format => :json}
      expect(response).to have_http_status(200)

      products_json = JSON.parse(response.body)
      expect(products_json.size).to eq(2)
   end
end

运行测试rake spec

得到错误：

NameError:
       uninitialized constant Product

创建model Product：

rails g model Product name:string description:text

rake db:migrate

运行测试rake spec

得到错误：

    Failure/Error: products_json = JSON.parse(response.body)
     JSON::ParserError:
       A JSON text must at least contain two octets!

这是因为我们的response不对，并且我们没有配置怎么获取json格式的输出。

创建文件: app/views/products/index.json.rabl

collection @products, :object_root => false
attributes :name

再次运行测试rake spec，测试通过

step3: 添加更多的字段

在 spec/products/products_controller_spec.rb中

products_json = JSON.parse(response.body)
expect(products_json.size).to eq(2)

expect(products_json[0][‘id‘]).to eq(1)
expect(products_json[1][‘id‘]).to eq(2)

expect(products_json[0][‘name‘]).to eq(‘apple juice‘)
expect(products_json[1][‘name‘]).to eq(‘banana juice‘)

expect(products_json[0][‘description‘]).to eq(‘good‘)
expect(products_json[1][‘description‘]).to eq(‘just so so‘)

expect(products_json[0][‘uri‘]).to end_with(‘/products/1‘)
expect(products_json[1][‘uri‘]).to end_with(‘/products/2‘)

在app/views/products/index.json.rabl中

collection @products, :object_root=>false
attributes :id, :name, :description

node :uri do |product|
   product_url product
end

4.GET /products => user get a product of specified id

step 1: 创建对应的controller方法，返回HTTP 200

添加测试：spec/products/products_controller_spec.rb

it ‘get product by product id‘ do
   get :show, {:id => 1}
   expect(response).to have_http_status(200)
end

对应修改：app/controllers/products_controller.rb

def show
   render :nothing => true
end

对应修改：config/routes.rb

resources :products do
   collection do
      get :index
   end

   member do
      get :show
   end
end

rake spec测试通过

step 2：创建对应的JSON显示

添加测试：spec/products/products_controller_spec.rb

before(:all) do
   #... ...
   @product = Product.new({:id => 1, :name => ‘apple juice‘, :description => ‘good‘})
end

it ‘get product by product id‘ do
   expect(Product).to receive(:find).with(1).and_return(@product).once

   get :show, {:id => 1, :format => :json}
   expect(response).to have_http_status(200)

   product_json = JSON.parse(response.body)
   expect(product_json[‘id‘]).to eq(1)
   expect(product_json[‘name‘]).to eq(‘apple juice‘)
   expect(product_json[‘description‘]).to eq(‘good‘)
   expect(product_json[‘uri‘]).to end_with(‘/products/1‘)
end

对应修改：app/controllers/products_controller.rb

def show
   @product = Product.find(params[:id].to_i)
end

Q:params[:id].to_i，为什么这里从测试代码过来的params[:id]它使一个string类型呢

添加JSON显示：app/views/products/show.json.rabl

object false

node(:id) { |product| @product.id }
node(:name) { |product| @product.name }
node(:description) { |product| @product.description }
node(:uri) { |product| product_url @product }

运行测试，通过

step 3：重构rabl

修改app/views/products/show.json.rabl

object @product

attributes :id, :name, :description

node(:uri) { |product| product_url product }

修改app/views/products/index.json.rabl

collection @products

extends ‘products/show‘

配置rabl：创建文件config/initializers/rabl_config.rb

Rabl.configure do |config|
   config.include_json_root = false
end

运行测试，通过，这样减少了rabl间的重复代码

step 4：HTTP 404

添加测试：spec/products/products_controller_spec.rb

it ‘get 404 when product not found‘ do
   expect(Product).to receive(:find).with(100).and_raise(ActiveRecord::RecordNotFound)

   get :show, {:id => 100, :format => :json}
   expect(response).to have_http_status(404)
end

对应修改：

class ProductsController < ApplicationController
   rescue_from ActiveRecord::RecordNotFound, with: :product_not_found

   #... ... 

   def show
      @product = Product.find(params[:id])
   end

   protected
      def product_not_found
         response.status = :not_found
      end
end

参考rescue_from

（更新中，欢迎指教）

将会要修改的部分是如何写好rspec，参考：http://betterspecs.org/