Mongoid Magic Counter Cache

Mongoid Counter Cache is a simple mongoid extension to add basic counter cache functionality to Embedded and Referenced Mongoid Documents.

http://rdoc.info/github/jah2488/mongoid-magic-counter-cache/master/frames

$ [sudo] gem install mongoid_magic_counter_cache

gem 'mongoid_magic_counter_cache'

First add a field to the document where you will be accessing the counter cache from.

class Library
  include Mongoid::Document

  field :name
  field :city
  field :book_count
  has_many :books

end

Then in the referrenced/Embedded document. Include Mongoid::MagicCounterCache

class Book
  include Mongoid::Document
  include Mongoid::MagicCounterCache

  field :first
  field :last

  belongs_to    :library
  counter_cache :library
end

$ @library.book_count
#=> 990

If you do not wish to use the model_count naming convention, you can override the defaults by specifying the :field parameter.

counter_cache :library, :field => "total_amount_of_books"

If you want to maintain counter based on certain condition, then you can specify it using :if

class Post 
  include Mongoid::Document

  field :article
  field :comment_count

  has_many :comments

end

Then in the referrenced/Embedded document, add condition for counter using :if

class Comment
  include Mongoid::Document
  include Mongoid::MagicCounterCache

  belongs_to :post

  field :remark
  field :is_published, type: Boolean, default: false

  counter_cache :post, :if => Proc.new { |act| (act.is_published)  }
end

comment_count will get incremented / decremented only when :if condition returns true

In conjunction with the conditional counter, if you want to maintain counter after an update to an object, then you can specify it using :if_update

Using same example as above, in the referrenced/Embedded document, add an additional condition for counter using :if_update

class Comment
  include Mongoid::Document
  include Mongoid::MagicCounterCache

  belongs_to :post

  field :remark
  field :is_published, type: Boolean, default: false

  counter_cache :post, :if => Proc.new { |act| (act.is_published)  }, :if_update => Proc.new { |act| act.changes['is_published'] }
end

When a comment is saved, comment_count will get incremented / decremented if the is_published field is dirty.

If you'd like to contribute, feel free to fork and merge until your heart is content