Counter_cache in ruby on rails 1.2.2

Posted on 08 June 2007

I came across a rather odd Rails gotcha today whilst trying to use the counter_cache method.

Counter cache is a magic field that you can use with belongs_to relationships to keep a count of how many related objects the parent has. In my case, how many photos a job has.

Basically everything was getting saved ok, but the counter wasn't getting updated until I discovered that I needed to reload the job object after i'd created the association and before the save.

def add    
    @photo = Photo.new(params[:photo])    
    return unless request.post?
    @job.photos << @photo
    @job.reload
    if @job.save    
      redirect_to photos_url
      flash[:notice] = "Photo uploaded"
    end
  end

I can only assume it is something Rails 1.2.2 related as i've definitely used counter_cache without the extra reload step in the past and it's not detailed in any examples of its' usage.

The reload feels like quite a dirty fix, but it does the job, hopefully this will save someone else the time I wasted trying to figure this out.

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Comments left...

• Thanks, very useful

  Nico Orellana at 07 Jul 07 at 01:38

• I knew I was missing something

  Matt at 18 Sep 07 at 05:44

• I have the following error. Any help would be appreciated.

  ActiveRecord::StatementInvalid: Mysql::Error: Unknown column ‘blog/comments_count’ in ‘field list’: UPDATE blog_posts SET `blog/comments_count` = `blog/comments_count` + 1 WHERE (`id` = 1)

  I have the following class:

  class Blog::Post < ActiveRecord::Base
  set_table_name ‘blog_posts’

  has_many :comments, :order => ‘created_at ASC’, :dependent => :destroy

  end

  —> I have a column in Blog::Post called ‘comments_counter’
  class Blog::Comment < ActiveRecord::Base
  belongs_to :post, :counter_cache => true

  end

  I don’k know why

  donny at 04 Dec 07 at 23:41

• column name is ‘comments_count’. sorry for the mispelling on the previous post.

  Donny at 04 Dec 07 at 23:43

• See, adding that reload doesn’t work for me though.

  fulvio at 29 Jan 08 at 19:46

• How to add counter_cache if I have has_many_polymorphs?
  For example:

  I have model Topic and Articles:

  in Topic

  has_many_polymorphs :affiliateds, :from => [:topics, :articles], :through => :affiliations, :dependent => :destroy, :as => :affiliate

  How to add topics_count, articles_count?

  MyTaskHelper at 17 Nov 08 at 09:22

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