How to avoid N+1 queries in Rails

Question

I have the following request in controller:

  def show
    @statistics = Keyword.find(params[:id]).statistics.order(:word).paginate :per_page => 10, :page => params[:page]
  end

And in one place of a view file I request a cache id parameter:

<td><%= link_to "Open", cache_path(stats.cache.id), :target => "_blank"  %></td>

Which produces N+1 queries like the following:

 Parameters: {"id"=>"1"}
  Keyword Load (0.5ms)  SELECT  "keywords".* FROM "keywords" WHERE "keywords"."id" = $1 LIMIT 1  [["id", 1]]
   (0.4ms)  SELECT COUNT(*) FROM "statistics" WHERE "statistics"."keyword_id" = $1  [["keyword_id", 1]]
  Statistic Load (0.4ms)  SELECT  "statistics".* FROM "statistics" WHERE "statistics"."keyword_id" = $1  ORDER BY "statistics"."word" ASC LIMIT 10 OFFSET 0  [["keyword_id", 1]]
  Cache Load (0.5ms)  SELECT  "caches".* FROM "caches" WHERE "caches"."statistic_id" = $1 LIMIT 1  [["statistic_id", 5]]
  Cache Load (0.6ms)  SELECT  "caches".* FROM "caches" WHERE "caches"."statistic_id" = $1 LIMIT 1  [["statistic_id", 4]]
  Cache Load (0.5ms)  SELECT  "caches".* FROM "caches" WHERE "caches"."statistic_id" = $1 LIMIT 1  [["statistic_id", 3]]
  Cache Load (0.7ms)  SELECT  "caches".* FROM "caches" WHERE "caches"."statistic_id" = $1 LIMIT 1  [["statistic_id", 2]]
  Cache Load (0.5ms)  SELECT  "caches".* FROM "caches" WHERE "caches"."statistic_id" = $1 LIMIT 1  [["statistic_id", 1]]
  Rendered statistics/show.html.erb within layouts/application (13.7ms)

Is there any way to avoid it?

You might have to, or even want to - http://stackoverflow.com/a/26251892/525478 — Brad Werth, Oct 11 '15 at 09:22

byakugie · Answer 1 · 2015-10-11T08:38:10.190

0

EDIT

ActiveRecord has a method called includes, which ensures that all the associated datas specified are loaded with the minimum number of queries.

def show
  @keyword = Keyword.find(params[:id])
  @statistics = @keyword.statistics.includes(:cache).order("statistics.word").paginate :per_page => 10, :page => params[:page]
end

edited Oct 11 '15 at 08:38

answered Oct 11 '15 at 08:10

byakugie

643
3
14

stats.cache.id (your codes) is different that stats.cache_id (mine) – byakugie Oct 11 '15 at 08:19
It throws out the following error: ``undefined method `cache_id' for #`` – Oct 11 '15 at 08:19
1

also I found good article about [N+1 Problem](http://www.sitepoint.com/silver-bullet-n1-problem/) – byakugie Oct 11 '15 at 08:42
[How to accept answer](http://meta.stackexchange.com/questions/5234/how-does-accepting-an-answer-work?lq=1) – byakugie Oct 12 '15 at 00:11

How to avoid N+1 queries in Rails

1 Answers1