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
http://github.com/flyerhzm/bullet.
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