Hi guys,
I wrote a plugin to detect the N+1 queries, it works very well and maybe helpful to you. The site of the plugin is GitHub - flyerhzm/bullet: help to kill N+1 queries and unused eager loading. The README is good to explain how to use the plugin and the spec/ bullet_association_spec.rb show you what are N+1 queries and what are not.
I will still give you an quick example to show how to use the plugin step by step:
1. setup test environment
$ rails test $ cd test $ script/generate scaffold post name:string $ script/generate scaffold comment name:string post_id:integer $ rake db:migrate
2. change app/model/post.rb and app/model/comment.rb
class Post < ActiveRecord::Base has_many :comments end
class Comment < ActiveRecord::Base belongs_to :post end
3. go to script/console and execute
post1 = Post.create(:name => 'first') post2 = Post.create(:name => 'second') post1.comments.create(:name => 'first') post1.comments.create(:name => 'second') post2.comments.create(:name => 'third') post2.comments.create(:name => 'fourth')
4. change the app/views/posts/index.html.erb to generate a N+1 query
<h1>Listing posts</h1>
<table> <tr> <th>Name</th> </tr>
<% @posts.each do |post| %> <tr> <td><%=h post.name %></td> <td><%= post.comments.collect(&:name) %></td> <td><%= link_to 'Show', post %></td> <td><%= link_to 'Edit', edit_post_path(post) %></td> <td><%= link_to 'Destroy', post, :confirm => 'Are you sure?', :method => :delete %></td> </tr> <% end %> </table>
<br />
<%= link_to 'New post', new_post_path %>
5. add bullet plugin
$ script/plugin install git://github.com/flyerhzm/bullet.git
6. enable the bullet plugin in development, add a line to config/ environments/development.rb
Bullet.enable = true
7. start server
$ script/server
8. input http://localhost:3000/posts in browser, then you will see a popup alert box says
The request has N+1 queries as follows: model: Post => associations: [comment]
which means there is a N+1 query from post object to comments associations.
In the meanwhile, there's a log appended into log/bullet.log file
2009-08-17 15:07:31[INFO] N+1 Query: PATH_INFO: /posts; model: Post => assocations: [comments]
The generated SQLs are
Post Load (1.0ms) SELECT * FROM "posts" Comment Load (0.4ms) SELECT * FROM "comments" WHERE ("comments".post_id = 1) Comment Load (0.3ms) SELECT * FROM "comments" WHERE ("comments".post_id = 2)
9. fix the N+1 query, change app/controllers/posts_controller.rb file
def index @posts = Post.find(:all, :include => :comments)
respond_to do |format| format.html # index.html.erb format.xml { render :xml => @posts } end end
10. refresh http://localhost:3000/posts page, no alert box and no log appended.
The generated SQLs are
Post Load (0.5ms) SELECT * FROM "posts" Comment Load (0.5ms) SELECT "comments".* FROM "comments" WHERE ("comments".post_id IN (1,2))
a N+1 query fixed. Cool!
Hope you like the plugin!
Thanks, Richard