Problem with counter cache in many-to-many relationship

aris · September 13, 2012, 3:52pm

Hi guys,
I am having trouble getting to counter cache to work properly with a
many-to-many relationship. What I have done is:

rails g scaffold post title:string body:text
rails g scaffold tag name:string taggings_count:integer
rails g model tagging post_id:integer tag_id:integer

Then I created the relationship as shown in my Gist:

gist.github.com

https://gist.github.com/halfdan/3710093

post.rb

class Post < ActiveRecord::Base
  attr_accessible :body, :title, :tag_names
  attr_reader :tag_names

  has_many :taggings
  has_many :tags, :through => :taggings

  def tag_names=(tag_list)
    tag_names = tag_list.gsub(/\s+/, "").split(",")
    existing = self.tags.map {|t| t.name }

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tag.rb

class Tag < ActiveRecord::Base
  attr_accessible :name

  has_many :taggings
end

tagging.rb

class Tagging < ActiveRecord::Base
  attr_accessible :post_id, :tag_id

  belongs_to :tag, :counter_cache => true, touch: true
  belongs_to :post
end

The idea is to have an input field when creating a post, where tags can
be
entered seperated by comma. The tag_names method then splits those tags,
adds new ones and deletes the ones that are now missing.

The counter_cache is correctly increased when adding a tag to the list.
However, decreasing the number after a tag removal does not work.

I have done some searching and found several blog articles (e.g.
http://whilefalse.net/2011/04/05/rails-3-counter-cache-has_many-through/)
explaining that this was a bug in Rails 3.0.x that has been addressed in
edge rails. See the old bug report on lighthouse:
https://rails.lighthouseapp.com/projects/8994/tickets/2824-patch-has_many-through-doesnt-update-counter_cache-on-join-model-correctly
and
then the fix on Github:
Correctly update counter caches on deletion for has_many :through [#2… · rails/rails@52f09ea · GitHub

Why am I still having this problem, when it was fixed two years ago? Am
I
missing something here?

FYI:

rails -v

Rails 3.2.8

Cheers,
Fabian