application_controller.rb

class ApplicationController < ActionController::Base
  # Overwrite Devise's authenticate_user! to store where they should be redirected back to
  def authenticate_user!(opts={})
    session[:user_return_to] = request.referrer
    super(opts)
  end

  # Change redirect after Devise login; defaults to root_url
  def after_sign_in_path_for(user)
    stored_location_for(user) || dashboard_path
  end
end