rails缓存－part1

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转自：http://www.railsenvy.com/

1 如果在开发模式下，缓寸是不可用的，需要改动配制启动缓存，在/config/environments/development.rb中设置
 

config.action_controller.perform_caching = true;

2 页面缓存
  页面缓存是Rails最为FASTEST的缓存机制，符合页面缓存的两种情况：
  * 如果同一页面对所有用户是相同的（If your page is the same for all users.）
  * If your page is available to the public, with no authentication needed.
  如果我的blog侧栏要显示最近的10篇文章。右不经常改动。为了提高性能，我可以把它缓存起来。

  class BlogController < ApplicationController
    caches_page :list
    def list
      Post.find(:all, :order => "created_on desc", :limit => 10)
    end
   ...

  caches_page告诉程序第一次"list"action被请求时，取得html结果，并存储在缓存文件里。
  The "caches_page" directive tells our application that next time the "list" action is requested, take the resulting html, and store it in a cached file.
 
  如过在mongrel中运行，第一次请求时在/logs/development.log文件中看到的日志为：
  Processing BlogController#list (for 127.0.0.1 at 2007-02-23 00:58:56) [GET]
  Parameters: {"action"=>"list", "controller"=>"blog"}
  SELECT * FROM posts ORDER BY created_on LIMIT 10
  Rendering blog/list
  Cached page: /blog/list.html (0.00000)    表示缓存文件被存储了。存储的位置在/public/blog/list.html
  Completed in 0.18700 (5 reqs/sec) | Rendering: 0.10900 (58%) | DB: 0.00000 (0%) | 200 OK [http://localhost/blog/list]
  缓存后，如果再次请求，就直接利用缓存的结果，这样比再次解释执行代码快上100倍

  同样的有：

  http://localhost:3000/blog/list => /public/blog/list.html
  http://localhost:3000/blog/edit/5 => /public/edit/5.html
  http://localhost:3000/blog => /public/blog.html
  http://localhost:3000/ => /public/index.html
  http://localhost:3000/blog/list?page=2 => /public/blog/list.html

 
3 怎样缓存分页页面：
  因为缓存会忽略额外的参数，所以形如："/blog/list?page=2"得不到想要的结果的，应该该成'/blog/list/2'，这就需要配置特殊的路由了。

  map.connect 'blog/list/:page',
    :controller => 'blog',
    :action => 'list',
    :requirements => { :page => /\d+/},
    :page => nil
  <%= link_to "Next Page", :controller => 'blog', :action => 'list', :page => 2 %>

　以上的方法就能解决分页缓存的问题了。

４清除缓存　
　如果新增了一篇blog后，希望能更新在侧栏的最进１０篇文章
　解决的方法是执行：

　expire_page(:controller => 'blog', :action => 'list')

　同样有

　expire_page(:controller => 'blog', :action => 'show', :id => 5)

５Sweepers
　Sweepers是一段代码，帮你自动清除内容以太旧的缓存文件，sweepers观察observe我们的一个或多个(model)，当model被添加／更新／删除时sweeper会得到通知，然后运行我们所期望的代码：
　Sweepers可以在controllers目录中创建，但还是可以添加到/config/environment.rb.

　Rails::Initializer.run do |config|
  　 # ...
  　 config.load_paths += %W( #{RAILS_ROOT}/app/sweepers )
  　 # ...
　end

　
　最好的方法是另外创建一个目录sweepers，把代码写在sweepers/blog_sweeper.rb文件中

class BlogSweeper < ActionController::Caching::Sweeper
  observe Post # This sweeper is going to keep an eye on the Post model

  # If our sweeper detects that a Post was created call this
  def after_create(post)
          expire_cache_for(post)
  end
  
  # If our sweeper detects that a Post was updated call this
  def after_update(post)
          expire_cache_for(post)
  end
  
  # If our sweeper detects that a Post was deleted call this
  def after_destroy(post)
          expire_cache_for(post)
  end
          
  private
  def expire_cache_for(record)
    # Expire the list page now that we posted a new blog entry
    expire_page(:controller => 'blog', :action => 'list')
    
    # Also expire the show page, incase we just edited a blog entry
    expire_page(:controller => 'blog', :action => 'show', :id => record.id)
  end
end

　下一步我们需要告诉controller当sweeper激活时

　class BlogController < ApplicationController
   caches_page :list, :show
   cache_sweeper :blog_sweeper, :only => [:create, :update, :destroy]