rails缓存－part2

上一部分介绍了页面缓存．这部分住要介绍Action缓存，Fragment缓存，ActiveRecord缓存
这几种缓存的效果为：

   1. Page Caching - Fastest
   2. Action Caching - Next Fastest
   3. Fragment Caching - Least Fast

１Action缓存
　Action缓存和页面缓存很相似，但会被过滤拦截．

　class BlogController < ApplicationController
  layout 'base'
  before_filter :authenticate  # <--- Check out my authentication
  caches_action :list, :show

　执行list action请求后，打出的日志为：

　Processing BlogController#list (for 127.0.0.1 at 2007-03-04 12:51:24) [GET]
　Parameters: {"action"=>"list", "controller"=>"blog"}
　Checking Authentication
　Post Load (0.000000) SELECT * FROM posts ORDER BY created_on LIMIT 10
　Rendering blog/list
　Cached fragment: localhost:3000/blog/list (0.00000)
　Completed in 0.07800 (12 reqs/sec) | Rendering: 0.01600 (20%) | DB: 0.00000 (0%) | 200 OK [http://localhost/blog/list]

　
　Action缓存生成的缓存文件存放在/tmp/cache/目录
　同时注意before_filters必须要放在caches_action前面

２Action缓存清除
　像页面缓存那样，只需要把"expire_page"该为"expire_action"在/app/sweepers/blog_sweeper.rb.文件中
　一次清楚Action Cache 和 Fragment cache的命令：rake tmp:cache:clear

３Fragment缓存
　Fragment缓存允许你在view中缓存部分代码片断．

　<strong>My Blog Posts</strong>
　<% cache do %>
 　 <ul>
    　<% for post in @posts %>
       　<li><%= link_to post.title, :controller => 'blog', :action => 'show', :id => post %></li>
     　<% end %>
  　</ul>
　<% end %>
　The "cache do" will create a fragment cache: 

/tmp/cache/localhost:3000/blog/list.cache
　从下的日志输出可以看出．缓存前后的执行的时间：

　Processing BlogController#list (for 127.0.0.1 at 2007-03-17 22:02:16) [GET]
　Authenticating User
 　 Post Load (0.000230)   SELECT * FROM posts
　Rendering blog/list
　Cached fragment: localhost:3000/blog/list (0.00267)
　Completed in 0.02353 (42 reqs/sec) | Rendering: 0.01286 (54%) | DB: 0.00248 (10%) | 200 OK [http://localhost/blog/list]


　Processing BlogController#list (for 127.0.0.1 at 2007-03-17 22:02:17) [GET]
　Authenticating User
  　Post Load (0.000219)   SELECT * FROM posts
　Rendering blog/list
　Fragment read: localhost:3000/blog/list (0.00024)
　Completed in 0.01530 (65 reqs/sec) | Rendering: 0.00545 (35%) | DB: 0.00360 (23%) | 200 OK [http://localhost/blog/list]

　不过从上面的日志可以看出执行了两次．需要去改变一下代码：

　def list
 　 unless read_fragment({})
   　 @post = Post.find(:all, :order => 'created_on desc', :limit => 10) %>
  　end
　end

４Fragment缓存清除．和前面一样：

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

　清楚多个页面缓存可以像下面那样：

　expire_fragment(:controller => 'blog', :action => 'list', :page => 1)
　expire_fragment(:controller => 'blog', :action => 'list', :page => 2)
　expire_fragment(:controller => 'blog', :action => 'list', :page => 3)

　更简单的方法为：
　expire_fragment(%r{blog/list.*})

５分页的片断缓存：
　在默认的情况下分页缓存的文件名像/localhost:3000/blog/list.cache．这样就导致覆盖了前面叶面的内容，这就需要去改变缓存文件的名字：

　 def list
    unless read_fragment({:page => params[:page] || 1})  # Add the page param to the cache naming
      @post_pages, @posts = paginate :posts, :per_page => 10
    end
  end

　我们可以这样写"read_fragment({:controller => 'blog', :action => 'list', :page => params[:page] || 1})" 但是默认情况下自动添加了这两个参数，就不再需要我门去添加了.
　在/views/blog/list.rhtml中
　<% cache ({:page => params[:page] || 1}) do %>
     ...  All of the html to display the posts ...
　<% end %>
运行后缓存的文件名就是/localhost:3000/blog/list.page=1.cache等

另外的命名例子

　　<% cache (:controller => "base", :action => "user_tasks", :user_id => session[:user_id]) do %>
     <ul>
         <% for task in Task.find_by_member_id(session[:user_id]) %>
           <li><%= task.name %></li>
         <% end %>
     </ul>
     <% end %> 

生成的缓存文件为：/localhost:3000/base/user_tasks.user_id=1.cache.
cache ("turkey") => "/tmp/cache/turkey.cache"
cache (:controller => 'blog', :action => 'show', :id => 1) => "/tmp/cache/localhost:3000/blog/show/1.cache"
cache ("blog/recent_posts") => "/tmp/cache/blog/recent_posts.cache"
cache ("#{request.host_with_port}/blog/recent_posts") => "/tmp/cache/localhost:3000/blog/recent_posts.cache"　

６Action/Fragment Cache缓存存储方式：
　页面缓存只能存储在文件中．Action/Fragment Cache有多中存储方式：
　１：文件存储
　２：内存存储
　３：DRb存储
　４：MemCache存储
在config/environment.rb:中更改存储方式

ActionController::Base.fragment_cache_store = :file_store,