Mongoid and counter_cache column

Question

I have Comment model:

class Comment
  include Mongoid::Document
  include Mongoid::Timestamps
  belongs_to :commentable, polymorphic: true, touch: true#, counter_cache: true

When I run:

Article.first.comments.count => 1 #without counter_cache: true

but with "counter_cache: true" I get :

Article.first.comments.count => NoMethodError: undefined method count' for nil:NilClass Article.first.comments => NoMethodError: undefined methodcount' for nil:NilClass

Has anyone encountered such problem?

score 6 · Answer 1 · answered Mar 24 '15 at 10:27

6

The complete solution for future reference is:

class Comment
  include Mongoid::Document
  belongs_to :commentable, polymorphic: true, touch: true, counter_cache: :comments_count
 end

class Article
  include Mongoid::Document
  field :comments_count, type: Integer
end

So don't forget to add the integer field to the parent model.

answered Mar 24 '15 at 10:27

David Backeus

455
6
8

1

Seems like `counter_cache: true` is not doing anything right with Mongoid so it's one of those key differences between AR and Mongoid that is badly documented in the official Rails doc. – Cyril Duchon-Doris Jan 15 '17 at 17:17

score 2 · Answer 2 · answered Nov 13 '13 at 22:48

2

Sloved with:

counter_cache: :comments_count

answered Nov 13 '13 at 22:48

FastIndian

222
4
12

score 0 · Answer 3 · answered Sep 15 '22 at 06:57

As with ActiveRecord, the :counter_cache option can be used on an association to make finding the number of belonging objects more efficient. Also similar to ActiveRecord, you must take into account that there will be an extra attribute on the associated model. This means that with Mongoid, you need to include Mongoid::Attributes::Dynamic on the associated model

https://www.mongodb.com/docs/mongoid/8.0/reference/associations/index.html#the-counter-cache-option

Mongoid and counter_cache column

3 Answers3