gem 'spleen'

bundle exec rails generate spleen:install

# edit app/models/article.rb:
  extend Spleen
  spleen(:dependent => :destroy)

# add Article to RATEABLE_TYPES on app/models/rating.rb:
  RATEABLE_TYPES = %w{Article}

a = Article.create(:title => 'test')
a.rate(1, User.last)
a.ratings # => [#<Rating id: 1, ...]
a.average_rate # => 1.0
a.sum_rate # => 1
a.count_rate # => 1

bundle exec ruby test/*_test.rb