Ruby on Rails，创建最简单的视图/控制器单元Hello World

在Ruby on Rails，创建一个最简单的站点中我们通过rails new simple_site命令创建了一个web应用骨架。笔墨纸砚都准备好了，该是时候写出第一个Hello World啦~！

Rails明确的按照MVC结构组织内容，回想一下MVC结构的简单知识。Browser（浏览器）向Controller（控制器）发出交互请求；Controller对请求做出分发处理调用Model（模型）进行业务或者数据运算；Controller将Model运算的结果推送给View（视图）使其在Browser中绘制显示。作为Hello World来说，建立一个从Browser到Controller再到View的例子既简单有很能说明问题。也就是说这个例子中不涉及与模型及数据库的任何操作，只是由Controller根据Browser发来的请求进行相应，并将相应交给View显示在Browser上。

进入应用目录simple_site，使用生成命令rails generate。这个命令负责在当前目录按照参数要求生成目录结构及代码。不带任何参数的命令会显示提示信息。

 E:\greensoft\RailsInstaller\Sites\simple_site>rails generate
 Usage: rails generate GENERATOR [args] [options]

 General options:
   -h, [--help]     # Print generator's options and usage
   -p, [--pretend]  # Run but do not make any changes
   -f, [--force]    # Overwrite files that already exist
   -s, [--skip]     # Skip files that already exist
   -q, [--quiet]    # Suppress status output

 Please choose a generator below.

 Rails:
   assets
   controller
   generator
   helper
   integration_test
   mailer
   migration
   model
   observer
   performance_test
   resource
   scaffold
   scaffold_controller
   session_migration
   task

 Coffee:
   coffee:assets

 Jquery:
   jquery:install

 Js:
   js:assets

 我们需要创建Controller和View，使用rails generate controller命令。不带任何参数的命令会对创建controller的使用方式进行提示，应该静下心来读一读。其中最有用的部分是说，以CamelCase（大写字母开头分割单词）或者under_scored（下划线分割单词）的方式命名Controller，将View名称列表以参数的方式给出。后面还举了一个很典型的例子。

 E:\greensoft\RailsInstaller\Sites\simple_site>rails generate controller
 Usage:
   rails generate controller NAME [action action] [options]

 Options:
       [--skip-namespace]        # Skip namespace (affects only isolated applications)
       [--old-style-hash]        # Force using old style hash (:foo => 'bar') on Ruby >= 1.9
   -e, [--template-engine=NAME]  # Template engine to be invoked
                                 # Default: erb
   -t, [--test-framework=NAME]   # Test framework to be invoked
                                 # Default: test_unit
       [--helper]                # Indicates when to generate helper
                                 # Default: true
       [--assets]                # Indicates when to generate assets
                                 # Default: true

 Runtime options:
   -f, [--force]    # Overwrite files that already exist
   -p, [--pretend]  # Run but do not make any changes
   -q, [--quiet]    # Supress status output
   -s, [--skip]     # Skip files that already exist

 Description:
     Stubs out a new controller and its views. Pass the controller name, either
     CamelCased or under_scored, and a list of views as arguments.

     To create a controller within a module, specify the controller name as a
     path like 'parent_module/controller_name'.

     This generates a controller class in app/controllers and invokes helper,
     template engine and test framework generators.

 Example:
     `rails generate controller CreditCard open debit credit close`

     Credit card controller with URLs like /credit_card/debit.
         Controller:      app/controllers/credit_card_controller.rb
         Functional Test: test/functional/credit_card_controller_test.rb
         Views:           app/views/credit_card/debit.html.erb [...]
         Helper:          app/helpers/credit_card_helper.rb

我们要创建一个名为demo的Controller，指向名为index的View。在这里可以使用g来代替generate，就像s代替service一样。回显信息告诉我们，rails为我们在app/controller目录中创建了一个名为demo_controller的Controller。app/views/目录中创建了一个名为demo的目录，目录中的index.html.erb对应View。

 E:\greensoft\RailsInstaller\Sites\simple_site>rails g controller demo index
       create  app/controllers/demo_controller.rb
        route  get "demo/index"
       invoke  erb
       create    app/views/demo
       create    app/views/demo/index.html.erb
       invoke  test_unit
       create    test/functional/demo_controller_test.rb
       invoke  helper
       create    app/helpers/demo_helper.rb
       invoke    test_unit
       create      test/unit/helpers/demo_helper_test.rb
       invoke  assets
       invoke    coffee
       create      app/assets/javascripts/demo.js.coffee
       invoke    scss
       create      app/assets/stylesheets/demo.css.scss

controller目录中名为demo的Controller里有一个名为index的方法，在在这里应该叫做action。这个叫index的action，对应views目录中名为index.html.erb的View。

 class DemoController < ApplicationController
   def index
   end
 end

修改一下页面内容

 <h1>Demo#index</h1>
 <p>Hello World!</p>

 <p>Find me in app/views/demo/index.html.erb</p>

代码编写完毕，启动web服务器。在浏览器地址栏中输入：localhost:3000/demo/index。里程碑！