Find tournament's players by categories

gistfile1.rb

class Tournament < ActiveRecord::Base
    #SELECT "players".* 
    #FROM "players" 
    #WHERE "players"."id" IN (
      #SELECT "players"."id" 
      #FROM "players" 
      #INNER JOIN "pairs" 
      #ON ("pairs"."player_id" = "players"."id" OR "pairs"."partner_id" = "players"."id") AND "pairs"."tournament_id" = 4)
  def player
    players = Player.arel_table
    pairs = Pair.arel_table
    condition = (pairs[:player_id].eq(player[:id]).or(pairs[:partner_id].eq(player[:id]))).and(pairs[:tournament_id].eq(self.id))
    Player.where(:id => Player.select(players[:id]).joins(:pairs).on(condition))
  end
end