Quick Ranking by attribute Rails/Heroku

#rails

#heroku

#sql

#performance

#postgres

#bulk-processing

Need to rank your users by a specific attribute?

window functions for the win!
http://www.postgresql.org/docs/8.4/static/functions-window.html

Make sure you enable heroku-postgresql:basic addon and we are talking milliseconds for thousands of users.

class User < ActiveRecord::Base

 def self.update_ranking
 sql = "update users
 set rank = d_rnk
 from (SELECT id, row_number() OVER (ORDER BY total_downloads DESC) as d_rnk FROM users) as ranked
 where ranked.id = users.id;"
 self.transaction do
 ActiveRecord::Base.connection.execute(sql)
 end
 end
end

rank(), deep_rank()