class User < ActiveRecord::Base
  has_many :scores, :order => 'score DESC',:autosave =>true,

  named_scope :top_score, :joins => :scores, :conditions => "scores.id is not null", :order => "scores.score DESC"
end


class Score < ActiveRecord::Base
  belongs_to :user
end


@users = User.top_score(:limit => 5)