诗歌rails之Rails eager loading

最新推荐文章于 2025-09-03 15:58:35 发布

转载最新推荐文章于 2025-09-03 15:58:35 发布 · 104 阅读

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原文链接：http://www.cnblogs.com/orez88/articles/1518466.html

文章标签：

#ruby #数据库

本文介绍了一种优化Rails应用程序性能的方法——Eager Loading。通过避免N+1查询问题，该技术可以显著提高应用效率。文章详细解释了如何在控制器中实现这一技术，并展示了使用前后对数据库查询次数的影响。

看这个页面代码:

ruby代码

<% for task in @tasks %>
<%= link_to task.name, task_path(task) %> in <%= task.project.name %>
<% end %>

<% for task in @tasks %>   <%= link_to task.name, task_path(task) %> in <%= task.project.name %> <% end %>

上面的代码对每个task对象，取得project的name属性并显示，看看log:

ruby代码

Project Lood (0.000131) SELECT * FROM projects WHERE (projects.id = 330)
Project Lood (0.000156) SELECT * FROM projects WHERE (projects.id = 330)
Project Lood (0.000136) SELECT * FROM projects WHERE (projects.id = 330)
Project Lood (0.000138) SELECT * FROM projects WHERE (projects.id = 330)
Project Lood (0.000133) SELECT * FROM projects WHERE (projects.id = 330)
Project Lood (0.000128) SELECT * FROM projects WHERE (projects.id = 330)
...
Completed in 0.14792 (6 reqs/sec) | ...

Project Lood (0.000131)  SELECT * FROM projects WHERE (projects.id = 330) Project Lood (0.000156)  SELECT * FROM projects WHERE (projects.id = 330) Project Lood (0.000136)  SELECT * FROM projects WHERE (projects.id = 330) Project Lood (0.000138)  SELECT * FROM projects WHERE (projects.id = 330) Project Lood (0.000133)  SELECT * FROM projects WHERE (projects.id = 330) Project Lood (0.000128)  SELECT * FROM projects WHERE (projects.id = 330) ... Completed in 0.14792 (6 reqs/sec) | ...

由于ActiveRecord默认是延迟加载的，这样对每个task对象去取project对象时又会查询一次数据库
对于这种情况，我们使用eager loading就比较合适了:

ruby代码

class TasksController < ApplicationController
def index
@tasks = Task.find(:all, :include => :project)
end
end

class TasksController < ApplicationController   def index     @tasks = Task.find(:all, :include => :project)   end end

:include指定我们将project属性一起查询出来，我们再看看log:

ruby代码

Task Lood Including Associations (0.000681) SELECT tasks.'id' AS t0_r0, tasks.'name' AS t0_r1, tasks.'project_id' AS
t0_r2, projects.'id' AS t1_r0, projects.'name' AS t1_r1 FROM tasks LEFT OUTER JOIN projects ON projects.id = tasks.pro
ject_id
...
Completed in 0.03464 (28 reqs/sec) | ...