environment

ubuntu 10.04
mongodb db version v2.0.2, pdfile version 4.5
ruby 1.9.2p180

i18n-0.6.0
multi_json-1.1.0
activesupport-3.2.2
builder-3.0.0
activemodel-3.2.2
bson-1.6.1
mongo-1.6.1
plucky-0.4.4
mongo_mapper-0.11.0

log

**Notice: C extension not loaded. This is required for optimum MongoDB Ruby driver performance.
  You can install the extension as follows:
  gem install bson_ext

  If you continue to receive this message after installing, make sure that the
  bson_ext gem is in your load path and that the bson_ext and mongo gems are of the same version.

MONGODB [DEBUG] Logging level is currently :debug which could negatively impact client-side performance. You should set your logging level no lower than :info in production.
MONGODB (0ms) admin['$cmd'].find({:ismaster=>1}).limit(-1)
MONGODB (0ms) test-db['users'].remove({})
MONGODB (0ms) test-db['users'].update({:_id=>BSON::ObjectId('4f6f0c3e121d923a61000001')}, {"_id"=>BSON::ObjectId('4f6f0c3e121d923a61000001'), "id"=>"1024", "name"=>"me"})
MONGODB (0ms) test-db['users'].find({}).limit(-1)
#<User _id: BSON::ObjectId('4f6f0c3e121d923a61000001'), id: "1024", name: "me">
MONGODB (0ms) test-db['users'].remove({:_id=>{"$in"=>["1024"]}})
MONGODB (0ms) test-db['users'].find({})
[#<User _id: BSON::ObjectId('4f6f0c3e121d923a61000001'), id: "1024", name: "me">]
MONGODB (0ms) test-db['users'].remove({:_id=>BSON::ObjectId('4f6f0c3e121d923a61000001')})
MONGODB (0ms) test-db['users'].find({})
[]

mongomapper_id_poc.rb

require 'mongo_mapper'

l = Logger.new(STDOUT)

MongoMapper.connection = Mongo::Connection.new('localhost', 27017, :logger => l)
MongoMapper.database = 'test-db'

class User
  include MongoMapper::Document

  key :id, String
  key :name, String
end

User.delete_all

User.create(:id => 1024, :name => 'me')

p user = User.first

user.delete

p User.all

User.delete_all(:_id => user._id)

p User.all