Question

How would you cache an ActiveResource model? Preferably in memcached. Right now it’s pulling a model from my REST API fine but it pulls dozens of records each time. Would be best to cache them.

Answer 1

I’ve been playing around with the same thing and I think I’ve found a pretty simple way to check redis for the cached object first. This will only work when you use the find method, but for my needs, I think this is sufficient.

By overriding find, I can check the checksum of the arguments to see if I already have the response saved in redis. If I do, I can pull the JSON response out of redis and create a new object right there. If I don’t, I’ll pass the find through to ActiveResource::Base’s find and the normal action will happen.

I haven’t implemented the saving of the responses into redis with ActiveResource yet, but my plan is to populate those caches elsewhere. This way, normally I can rely on my caches being there, but if they aren’t, I can fall back to the API.

class MyResource < ActiveResource::Base
  class << self
    def find(*arguments)
      checksum = Digest::MD5.hexdigest(arguments.md5key)
      cached = $redis.get "cache:#{self.element_name}:#{checksum}"
      if cached
        return self.new JSON.parse(cached)
      end

      scope   = arguments.slice!(0)
      options = arguments.slice!(0) || {}
      super scope, options
    end
  end
end

and a little patch so we can get an md5key for our array:

require 'digest/md5'

class Object
  def md5key
    to_s
  end
end

class Array
  def md5key
    map(&:md5key).join
  end
end

class Hash
  def md5key
    sort.map(&:md5key).join
  end
end

Does that help?