example of filtering scope in controller

gistfile1.rb

class PlayersController < ActiveController::Base
  before_filter :player_scope, except: :create
  
  def index
    respond_with(@players = @scope.all)
  end
  
  def show
    respond_with(@player = @scope.find(params[:id])
  end
  
protected
  def player_scope
    @scope = if params[:game_id]
      Game.find(params[:game_id]).players
    else
      Player
    end
  end
end