ActiveRecord::HasCount

N+1 count query killer for ActiveRecord
ActiveRecord::HasCount allows you to cache count of associated records by eager loading

Why ActiveRecord::HasCount?

Rails provides a way to resolve N+1 count query, which is belongs_to's counter_cache option.
It requires a column to cache the count. But adding a column just for count cache is overkill.

Thus this plugin enables you to preload counts in the same way as has_many and belongs_to.
has_count is an ActiveRecord's association, which is preloadable by preload or includes.

Installation

Add this line to your application's Gemfile:

gem 'activerecord-has_count'

Usage

Add has_count scope

First, call has_count with an association whose count you want to preload

class Tweet
  has_many :replies
  has_count :replies # defines association named :replies_count
end

The option creates an additional association whose name is replies_count.
Its association type is not an ordinary one (i.e. has_many, belongs_to) but has_count.

Preload the association

This association works well by default.

@tweets = Tweet.all
@tweets.each do |tweet|
  p tweets.replies_count # same as tweets.replies.count
end

You can eagerly load has_count association by includes or preload.

@tweets = Tweet.preload(:replies_count)
@tweets.each do |tweet|
  p tweets.replies_count # this line doesn't execute an additional query
end

Since it is association, you can preload nested has_count association.

@favorites = Favorite.preload(tweet: :replies_count)
@favorites.each do |favorite|
  p favorite.tweet.replies_count # this line doesn't execute an additional query
end

Contributing

1. Fork it ( https://github.com/k0kubun/activerecord-has_count/fork )
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 a new Pull Request