Very Slow MM time handling

Gemfile

source :rubygems

MONGO_VERSION = '~>1.6'

gem 'bson',     MONGO_VERSION
gem 'bson_ext', MONGO_VERSION
gem 'mongo',    MONGO_VERSION
gem 'mongo_mapper', "0.11.1"

test.rb

require "rubygems"
require "bundler/setup"
require "mongo_mapper"

MongoMapper.connection = Mongo::Connection.new('127.0.0.1', 27017)
MongoMapper.database = "test_times"

puts "Bundled"

class NoTimes
  include MongoMapper::Document
  key :astring, String
end


class Times
  include MongoMapper::Document
  key :atime, Time
end

puts "Creating test documents"

[NoTimes, Times].each &:delete_all

1000.times do
  NoTimes.create( astring: "A string")
  Times.create( atime: Time.now)
end

puts "Testing retrieval"

def bench( message, times=10 )
  t = Time.now
  times.times do
    yield
  end
  puts "#{message}: #{Time.now - t}"
end

bench "NoTimes MM" do
  NoTimes.all
end

bench "Times MM" do
  Times.all
end

bench "NoTimes Raw" do
  NoTimes.collection.find( {} ).map {|i| i}
end
bench "Times Raw" do
  Times.collection.find( {} ).map {|i| i}
end

test.rb.out

└─▪ ruby test.rb
Bundled
Creating test documents
Testing retrieval
NoTimes MM: 0.800193
Times MM: 1.393776
NoTimes Raw: 0.275042
Times Raw: 0.320742