impress/app/controllers/contributions_controller.rb

class ContributionsController < ApplicationController
  def index
    if params[:user_id]
      @user = User.find params[:user_id]
      @contributions = @user.contributions
    else
      @contributions = Contribution.includes(:user)
    end
    @contributions = @contributions.recent.paginate :page => params[:page]
    Contribution.preload_contributeds_and_parents @contributions
  end
end