Sin < ActiveRecord::Base

irb session

[75] pry(main)> def_memoized(:fac) {|x| x==0?1:x*fac(x-1) }
=> #<Proc:0x000000062147a0@/home/rgraham/working/cmportal/app/models/memoized_result.rb:7 (lambda)>
[76] pry(main)> fac(5)
  MemoizedResult Load (0.6ms)  SELECT `memoized_results`.* FROM `memoized_results` WHERE `memoized_results`.`key` = 'Object#fac(5)' LIMIT 1
  MemoizedResult Load (0.7ms)  SELECT `memoized_results`.* FROM `memoized_results` WHERE `memoized_results`.`key` = 'Object#fac(4)' LIMIT 1
  MemoizedResult Load (0.5ms)  SELECT `memoized_results`.* FROM `memoized_results` WHERE `memoized_results`.`key` = 'Object#fac(3)' LIMIT 1
  MemoizedResult Load (0.3ms)  SELECT `memoized_results`.* FROM `memoized_results` WHERE `memoized_results`.`key` = 'Object#fac(2)' LIMIT 1
  MemoizedResult Load (0.2ms)  SELECT `memoized_results`.* FROM `memoized_results` WHERE `memoized_results`.`key` = 'Object#fac(1)' LIMIT 1
  MemoizedResult Load (0.2ms)  SELECT `memoized_results`.* FROM `memoized_results` WHERE `memoized_results`.`key` = 'Object#fac(0)' LIMIT 1
   (0.1ms)  BEGIN
  SQL (0.3ms)  INSERT INTO `memoized_results` (`created_at`, `key`, `result`, `updated_at`) VALUES ('2012-12-05 15:05:38', 'Object#fac(0)', '[1]', '2012-12-05 15:05:38')
   (72.7ms)  COMMIT
   (0.1ms)  BEGIN
  SQL (0.4ms)  INSERT INTO `memoized_results` (`created_at`, `key`, `result`, `updated_at`) VALUES ('2012-12-05 15:05:38', 'Object#fac(1)', '[1]', '2012-12-05 15:05:38')
   (100.0ms)  COMMIT
   (0.1ms)  BEGIN
  SQL (0.4ms)  INSERT INTO `memoized_results` (`created_at`, `key`, `result`, `updated_at`) VALUES ('2012-12-05 15:05:38', 'Object#fac(2)', '[2]', '2012-12-05 15:05:38')
   (368.7ms)  COMMIT
   (0.1ms)  BEGIN
  SQL (0.4ms)  INSERT INTO `memoized_results` (`created_at`, `key`, `result`, `updated_at`) VALUES ('2012-12-05 15:05:38', 'Object#fac(3)', '[6]', '2012-12-05 15:05:38')
   (63.6ms)  COMMIT
   (0.1ms)  BEGIN
  SQL (0.4ms)  INSERT INTO `memoized_results` (`created_at`, `key`, `result`, `updated_at`) VALUES ('2012-12-05 15:05:38', 'Object#fac(4)', '[24]', '2012-12-05 15:05:38')
   (29.9ms)  COMMIT
   (0.2ms)  BEGIN
  SQL (0.5ms)  INSERT INTO `memoized_results` (`created_at`, `key`, `result`, `updated_at`) VALUES ('2012-12-05 15:05:39', 'Object#fac(5)', '[120]', '2012-12-05 15:05:39')
   (54.9ms)  COMMIT
=> 120
[77] pry(main)> fac(5)
  MemoizedResult Load (0.6ms)  SELECT `memoized_results`.* FROM `memoized_results` WHERE `memoized_results`.`key` = 'Object#fac(5)' LIMIT 1
=> 120

memoized_result.rb

class MemoizedResult < ActiveRecord::Base
  attr_accessible :key, :result
end

class Object
  def def_memoized(name, &block)
    self.class.send(:define_method, name) do |*args|
      args_str = args.map(&:to_s).join(',')
      key = "#{self.class}##{name}(#{args_str})"
      result = MemoizedResult.where(key: key).first
      if result
        ActiveSupport::JSON.decode(result.result).first
      else
        result = block.call(*args)
        enc_result = ActiveSupport::JSON.encode [result]
        MemoizedResult.create(key: key, result: enc_result)
        result
      end
    end
  end
end