请看
Rails里的Magic Column Names
这次就是讲用_count字段来缓存has_many的计数
看Project和Task的例子:
<h1>Projects</h1>
<table>
<% for project in @projects %>
<tr>
<td><%= link_to project.name, poject_path(project) %></td>
<td><small>(<%= pluralize project.tasks.size, 'task' %>)</small></td>
</tr>
<% end %>
</table>
上面的页面代码对所有的@projects显示tasks.size,看下log:
SQL (0.006385) SELECT count(*) AS count_all FROM tasks WHERE (tasks.project_id = 326)
SQL (0.000220) SELECT count(*) AS count_all FROM tasks WHERE (tasks.project_id = 327)
SQL (0.000383) SELECT count(*) AS count_all FROM tasks WHERE (tasks.project_id = 328)
SQL (0.000197) SELECT count(*) AS count_all FROM tasks WHERE (tasks.project_id = 329)
SQL (0.000215) SELECT count(*) AS count_all FROM tasks WHERE (tasks.project_id = 330)
上面显示了对每个project都使用SQL来count tasks,我们采用eager loading看看能否改进性能:
class ProjectsController < ApplicationController
def index
@projects = Project.find(:all, :include => :tasks)
end
end
再来看看log:
Project Lood Incluing Associations (0.000954) SELECT projects.'id' AS t0_r0, projects.'name' AS t0_r1, tasks.'id'
AS t1_r0, tasks.'name' AS t1_r1, tasks.'project_id' AS t1_r2 FROM projects LEFT OUTER JOIN tasks ON tasks.project
_id = projects.id
我们看到,使用eager loading确实只用一条SQL语句就完成工作,但是缺点是把tasks表所有的字段信息都取出来了,很多信息是
没有用的。
我们来看看更好的解决方案:
ruby script/generate migration add_tasks_count
我们新建一个migration,给projects表添加一个叫tasks_count的列:
class AddTasksCount < ActiveRecord::Migration
def self.up
add_column :projects, :tasks_count, :integer, :default => 0
Project.reset_column_information
Project.find(:all).each do |p|
p.update_attribute :tasks_count, p.tasks.length
end
end
def self.down
remove_column :projects, :tasks_count
end
end
我们还需要告诉Task类开启counter cache:
class Task < ActiveRecord::Base
belongs_to :projects, :counter_cache => true
end
好了,我们把ProjectsController的index方法改回lazy loading,刷新页面,再看看log:
Project Lood (0.000295) SELECT * FROM projects
可以看出,现在数据库只查询projects表的所有字段,查询时间也比前面的方案都短,性能大大提升。
分享到:
相关推荐
Rails::API 是 Rails 的精简版本,针对不需要使用完整 Rails 功能的开发者。 Rails::API 移除了 ActionView 和其他一些渲染功能,不关心Web前端的开发者可更容易、快速地开发应用程序,因此运行速度比正常的 Rails ...
使用Rails构建可伸缩和可维护API的最佳方法
#<ActiveSupport::Cache::Strategy::LocalCache::Middleware:0x164feb> Rack::Runtime Rack::MethodOverride ActionDispatch::RequestId Rails::Rack::Logger ActionDispatch::ShowExceptions ActionDispatch::...
Rails::Cache::Extended 这允许为记录集合生成自动过期的缓存键 安装 将此行添加到应用程序的 Gemfile 中: gem 'rails-cache-extended' 然后执行: $ bundle 或者自己安装: $ gem install rails-cache-...
Rails Cache 博文链接:https://mmm.iteye.com/blog/134696
反文化 Turbo为您的Rails应用程序提供计数器缓存。 对Rails标准计数器缓存的巨大改进...product.categories_count # => will use counter cache without query 安装 将counter_culture添加到您的Gemfile中: gem 'co
Ruby.on.Rails.Tutorial,Learn.Web.Development.with.Rails,Third.Edition-中文版 文字版.pdf 个人收集电子书,仅用学习使用,不可用于商业用途,如有版权问题,请联系删除!
《Rails之道》按照Rails的各个子系统进行组织编排,分别介绍了Rails的环境、初始过程、配置和日志记录,Rails的分配器、控制器、页面生成和路由,REST、资源和Rails,ActiveRecord的基础、关联、验证和高级技巧,...
webpack-rails, 将 web pack与你的Ruby on Rails 应用程序集成 不再维护webpack-rails 不再被维护。 有关详细信息,请参阅 #90. web pack-railsweb pack 为你提供了将 web pack集成到现有的Ruby on Rails 应用程序中...
[Pragmatic Bookshelf] Crafting Rails Applications Expert Practices for Everyday Rails Development (E-Book) ☆ 图书概要:☆ Rails 3 is a huge step forward. You can now easily extend the framework, ...
NULL 博文链接:https://lzqustc.iteye.com/blog/439128
初学 Ruby on Rails 必备之宝典
minitest-rails, Rails的Minitest集成 minitestRails 5的Minitest集成 安装gem install minitest-rails这将安装以下宝石:minitest配置创建一个新的Rail
提供用于Rails 4.x(及更高版本)资产管道的Sprockets实现。 安装 gem 'sprockets-rails' , :require => 'sprockets/railtie' 或者,如果禁用了Bundler自动请求功能,则在config/application.rb require 'sprockets...
Ruby on Rails Guides v2 - Ruby on Rails 4.2.5
Redis Store为现代Ruby框架提供了全套存储( Cache , I18n , Session , HTTP Cache ),例如: Ruby on Rails , Sinatra , Rack , Rack :: Cache和I18n 。 它支持对象编组,超时,单个或多个节点以及名称空间...
Challenges in styling a Rails application traditionally 23 Summary 24 Chapter 2: Introducing Bootstrap 3 25 What is Bootstrap? 26 Installing Bootstrap in a Rails project 27 Placing Bootstrap files in ...
Component-Based Rails Applications: Large Domains Under Control (Addison-Wesley Professional Ruby Series) By 作者: Stephan Hagemann ISBN-10 书号: 0134774582 ISBN-13 书号: 9780134774589 Edition 版本: ...