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
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
（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/