cache.rb

module Feeds
  module Cache
    extend ActiveSupport::Concern

    module InstanceMethods
      def redis_client
        uri = URI.parse(ENV["REDISTOGO_URL"] || "http://localhost:6379/")
        @redis ||= Redis.new(host: uri.host, port: uri.port, password: uri.password)
      end
    end

    def cache_result(*symbols)
      symbols.each do |symbol|
        original_method = :"_uncached_#{symbol}"

        class_eval <<-EOS, __FILE__, __LINE__ + 1
          include InstanceMethods

          alias #{original_method} #{symbol}

          def #{symbol}
            key = "feeds:cache:" + self.class.to_s.underscore
            if cache = redis_client.get(key)
              JSON.parse(Marshal.load(cache.unpack("m")[0]))
            else
              result = #{original_method}
              redis_client.set(key, [ Marshal.dump(result.to_json) ].pack("m"))
              result
            end
          end
        EOS
      end
    end
  end
end

cache_spec.rb

require "active_support/all"
require File.dirname(__FILE__) + "/../../../lib/feeds/cache"

class Redis
  def initialize(params)
  end

  def set(key, value)
    value
  end
end

class TestFeed
  extend Feeds::Cache

  def raw_data
    { "data" => "special_data" }
  end
  cache_result :raw_data
end

module Feeds
  describe Cache do
    it "when there is no cached result, cache the result" do
      Redis.any_instance.should_receive(:get).and_return(nil)
      Redis.any_instance.should_receive(:set).and_return(true)
      TestFeed.new.raw_data.should == { "data" => "special_data" }
    end

    it "when is a cached result, return the cache" do
      Redis.any_instance.should_receive(:get).and_return("BAhJIhx7ImRhdGEiOiJzcGVjaWFsX2RhdGEifQY6BkVG\n")
      TestFeed.new.raw_data.should == { "data" => "special_data" }
    end
  end
end