How to implement a Counter Cache in Rails?

ruby-on-rails one-to-many counter-cache
Yuval Karmi picture Yuval Karmi · Jun 2, 2010 · Viewed 7.8k times · Source

I have a posts controller and a comments controller. Post has many comments, and comments belong to Post. The associate is set up with the counter_cache option turned on as such:

#Inside post.rb
has_many :comments

#Inside comment.rb
belongs_to :post, :counter_cache => true

I have a comments_count column in my posts table that is defaulted to zero, as such:

add_column :posts, :comments_count, :integer, :default => 0

In the create action of my comments controller, I have the following code:

def create
  @posts = Post.find(params[:post_id])
  @comment = @post.comments.build(params[:comment])
  if @comment.save
    redirect_to root
  else
    render :action => 'new'
  end
end

My problem: when @comment.save is called, I get the following error:

ArgumentError in CommentsController#create

wrong number of arguments (2 for 0)

Removing :counter_cache => true from comment.rb completely solves the problem, so I'm assuming that it is the cause of this vague error. What am I missing here? How can I save my comment and still have rails take care of my counter_cache for my post?

Thanks!

Update - Application trace attached:

/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/base.rb:987:in `update_all'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/base.rb:987:in `update_counters_without_lock'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/locking/optimistic.rb:176:in `update_counters'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/base.rb:1006:in `increment_counter'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/associations.rb:1367:in `belongs_to_counter_cache_after_create_for_feed_entry'
/Library/Ruby/Gems/1.8/gems/activesupport-2.3.8/lib/active_support/callbacks.rb:178:in `send'
/Library/Ruby/Gems/1.8/gems/activesupport-2.3.8/lib/active_support/callbacks.rb:178:in `evaluate_method'
/Library/Ruby/Gems/1.8/gems/activesupport-2.3.8/lib/active_support/callbacks.rb:166:in `call'
/Library/Ruby/Gems/1.8/gems/activesupport-2.3.8/lib/active_support/callbacks.rb:93:in `run'
/Library/Ruby/Gems/1.8/gems/activesupport-2.3.8/lib/active_support/callbacks.rb:92:in `each'
/Library/Ruby/Gems/1.8/gems/activesupport-2.3.8/lib/active_support/callbacks.rb:92:in `send'
/Library/Ruby/Gems/1.8/gems/activesupport-2.3.8/lib/active_support/callbacks.rb:92:in `run'
/Library/Ruby/Gems/1.8/gems/activesupport-2.3.8/lib/active_support/callbacks.rb:276:in `run_callbacks'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/callbacks.rb:344:in `callback'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/callbacks.rb:267:in `create'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/base.rb:2915:in `create_or_update_without_callbacks'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/callbacks.rb:250:in `create_or_update'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/base.rb:2573:in `save_without_validation'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/validations.rb:1090:in `save_without_dirty'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/dirty.rb:79:in `save_without_transactions'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/transactions.rb:229:in `send'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/transactions.rb:229:in `with_transaction_returning_status'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/connection_adapters/abstract/database_statements.rb:136:in `transaction'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/transactions.rb:182:in `transaction'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/transactions.rb:228:in `with_transaction_returning_status'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/transactions.rb:196:in `save'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/transactions.rb:208:in `rollback_active_record_state!'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/transactions.rb:196:in `save'
/Users/yuval/Sites/rails/blog/app/controllers/comments_controller.rb:6:in `create'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/base.rb:1331:in `send'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/base.rb:1331:in `perform_action_without_filters'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/filters.rb:617:in `call_filters'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/filters.rb:610:in `perform_action_without_benchmark'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/benchmarking.rb:68:in `perform_action_without_rescue'
/Library/Ruby/Gems/1.8/gems/activesupport-2.3.8/lib/active_support/core_ext/benchmark.rb:17:in `ms'
/Library/Ruby/Gems/1.8/gems/activesupport-2.3.8/lib/active_support/core_ext/benchmark.rb:17:in `ms'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/benchmarking.rb:68:in `perform_action_without_rescue'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/rescue.rb:160:in `perform_action_without_flash'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/flash.rb:151:in `perform_action'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/base.rb:532:in `send'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/base.rb:532:in `process_without_filters'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/filters.rb:606:in `process'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/base.rb:391:in `process'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/base.rb:386:in `call'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/routing/route_set.rb:438:in `call'

Notice the only line that doesn't have to do directly with the Rails framework is:

/Users/yuval/Sites/rails/blog/app/controllers/comments_controller.rb:6:in `create'

Line 6 is the following:

if @comment.save

EDIT 2: the @posts/@post is a typo on my end when writing a simplified example for StackOverflow, my actual application doesn't have mistake.

Inspecting @comment, it seems to be completely valid - it returns back exactly what I expect it to - a new instance of comment with whatever information I passed to it with build. It only blows up when the save method is called on it.

Thank you for all the suggestions so far. Any other ideas?

Answer

Joshua Pinter picture Joshua Pinter · Jun 11, 2010

I ran through a sample rails app with your code and it all worked fine for me.

I would suggest debugging a little more like hurikhan77 is suggesting and see if it is just the @posts / @post issue that dain suggested.

Also, try creating a post and a comment in the console with some very simple content to see if it is working. 

$ ruby script/console

# add whatever fields are necessary to create     
> @p = Post.create(:title => "TestPost1")
  # => #<Post id: 3, ...

# again, add whatever is necessary to create
> @c = @p.comments.create(:comment => "TestComment1")
  # => #<Comment id: 8, ...

> Post.find(:last).comments_count
  # => 1

See what that gets you.

/ JP

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