cache_of_today.rb

class ApplicationController < ActionController::Base

  helper_method :count_something

  def count_something
    cache_of_today "count-of-something" do
      Something.count
    end
  end

  def cache_of_today(key, &block)
    cached = Rails.cache.read key
    if !cached || cached[:created_at] < 1.day.ago
      Rails.cache.write key, :created_at => Time.now, :value => block.call
      cached = Rails.cache.read key
    end
    cached[:value]
  end
end