Voting and ranking used in GitHeroes

global_leaderboard.rb

def self.leaderboard
  Hero.select("id, login, name, location, votes_received, avatar_url, html_url, rank() over(order by votes_received DESC)").limit(20)
end

leaderboard_by_location.rb

def self.leaderboard_by_location(location)
  Hero.select("id, login, name, location, votes_received, avatar_url, html_url, rank() OVER(PARTITION BY location ORDER BY votes_received DESC)").where("location = ?", location).limit(20)
end

query_plan_for_global_leaderboard.sql

Limit  (cost=0.00..6.52 rows=20 width=227) (actual time=0.039..0.123 rows=20 loops=1)
 ->  WindowAgg  (cost=0.00..157.07 rows=482 width=227) (actual time=0.037..0.116 rows=20 loops=1)
     ->  Index Scan Backward using desc_votes_recvd_idx on heros  (cost=0.00..149.84 rows=482 width=227) (actual time=0.020..0.059 rows=20 loops=1)
 Total runtime: 0.191 ms
(4 rows)

vote.rb

class Vote < ActiveRecord::Base
  belongs_to  :votee, :class_name => 'Hero', :counter_cache => :votes_received
  belongs_to  :voter, :class_name => 'Hero'

  validates_presence_of   :voter_id, :votee_id
  validates_uniqueness_of :voter_id,  :scope => :votee_id

  validate :check_if_hero_votes_for_himself

  def check_if_hero_votes_for_himself
    errors.add(:votee_id, "You can't vote for yourself, unfortunately") if votee_id == voter_id
  end

end