MongoidCounterCache Build Status

This gem is used to maintain a cached counter of an object's children, this avoids N + 1 queries issues when doing a count in a loop.

This is basically an implementation of ActiveRecord counter cache for Mongoid.

Installation

Add this line to your application's Gemfile:

gem 'mongoid_countercache'

And then execute:

$ bundle

Or install it yourself as:

$ gem install mongoid_countercache

Usage

Include Mongoid::CounterCache into your embedded or referenced model :

class Comment
  include Mongoid::Document
  include Mongoid::CounterCache

  belongs_to :post

  counter_cache :post
end

Heads up ! Be sure to declare the field in the parent model, due to dependency restrictions, it can't be added programatically without having the children model to be required first

class Post
  has_many :comments

  field :comment_count, :type => Integer, :default => 0
end

Use the count method in the parent model :

Post.first.comment_count

You can rename the field used for storing the counter

counter_cache :post, :field_name => 'comment_counter'

Then :

Post.first.comment_counter

Variants

Sometimes you want to keep a count but only for a subset of your document.

Fortunately, mongoid_counter_cache allows to keep alternative counters :

Don't forget to add in the Post class :

field :comment_count_positive, :type => Integer, :type => 0
field :comment_count_negative, :type => Integer, :type => 0

class Comment
  include Mongoid::Document
  include Mongoid::CounterCache

  field :mark, :type => Integer

  belongs_to :post

  counter_cache :post, :variants => {
    :positive => lambda { mark >= 8 },
    :negative => lambda { mark <= 2 }
  }
end

You just have to suffix the count method to get the number of positive comments here :

Post.first.comment_count_positive
Post.first.comment_count_negative

It's even magic ! If you update the comment so it doesn't belongs to the same counter, the counters will be updated accordingly.

Contributing

  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request