怎么使用Engine的

http://guides.rubyonrails.org/engines.html

1. rails plugin new engine_name —mountable
2. gem ‘engine_name’, path: “engine_path”
3. mount EngineName::Engine, at: ‘engine_name’

那么Engine做了什么

1. isolate_namespace
2. app
3. routes
4. initializers

isolate_namespace

用命名空间来隔离不同的engine

1. 设置railtie_name为 engine_name
2. 设置routes的default_scope为 engine_name
3. 其他

app

An instance of ActionDispatch::MiddlewareStack used to store middlewares.

routes

An instance of ActionDispatch::Routing::RouteSet used to store routes.

initializers

有如下这些initializers：

1. set_load_path before: :bootstrap_hook

    #将configred load paths 添加到 ruby load paths
    initializer :set_load_path, before: :bootstrap_hook do
      _all_load_paths.reverse_each do |path|
        $LOAD_PATH.unshift(path) if File.directory?(path)
      end
      $LOAD_PATH.uniq!
    end
   

2. set_autoload_paths :bootstrap_hook

    #暂时不能理解，简单的认为是那些自动加载的文件
    #包括["app"，"app/controllers", "app/helpers", "app/models",
    #    "app/mailers", "app/controllers/concerns", "app/models/concerns"]
    initializer :set_autoload_paths, before: :bootstrap_hook do
      ActiveSupport::Dependencies.autoload_paths.unshift(*_all_autoload_paths)
      ActiveSupport::Dependencies.autoload_once_paths.unshift(*_all_autoload_once_paths)
   
      # Freeze so future modifications will fail rather than do nothing mysteriously
      config.autoload_paths.freeze
      config.eager_load_paths.freeze
      config.autoload_once_paths.freeze
    end
   

3. add_routing_paths

    #加载路由文件
    initializer :add_routing_paths do |app|
      paths = self.paths["config/routes.rb"].existent
   
      if routes? || paths.any?
        app.routes_reloader.paths.unshift(*paths)
        app.routes_reloader.route_sets << routes
      end
    end
   

4. add_locales

    #I18n文件
    initializer :add_locales do
      config.i18n.railties_load_path.concat(paths["config/locales"].existent)
    end
   

5. add_view_paths

    #views文件为lazily load files
    #用ActiveSupport.on_load(name, options, block)，定义一个名为name的lazily load hook
    #之后可以ActiveSupport.run_load_hooks(name, base)来加载（让base来调用block）
    initializer :add_view_paths do
      views = paths["app/views"].existent
      unless views.empty?
        ActiveSupport.on_load(:action_controller){ prepend_view_path(views) if respond_to?(:prepend_view_path) }
        ActiveSupport.on_load(:action_mailer){ prepend_view_path(views) }
      end
    end
   

6. load_environment_config before: :load_environment_hook, group: :all

    #加载environments文件
    initializer :load_environment_config, before: :load_environment_hook, group: :all do
      paths["config/environments"].existent.each do |environment|
        require environment
      end
    end
   

7. append_assets_path, group: :all

    #加载assets文件
    initializer :append_assets_path, group: :all do |app|
      app.config.assets.paths.unshift(*paths["vendor/assets"].existent_directories)
      app.config.assets.paths.unshift(*paths["lib/assets"].existent_directories)
      app.config.assets.paths.unshift(*paths["app/assets"].existent_directories)
    end
   

8. prepend_helpers_path

    #加载helpers文件
    initializer :prepend_helpers_path do |app|
      if !isolated? || (app == self)
        app.config.helpers_paths.unshift(*paths["app/helpers"].existent)
      end
    end
   

9. load_config_initializers

    #加载config/initializers文件
    initializer :load_config_initializers do
      config.paths["config/initializers"].existent.sort.each do |initializer|
        load(initializer)
      end
    end
   

10. engines_blank_point

    #空白的initializer