Beware object ids in mongo mapper

gem "mongo", "1.0"
gem "bson_ext", "1.0"
gem "mongo_ext", "0.19.3"
gem "mongo_mapper", "0.7.5"

require 'mongo_mapper'

MongoMapper.database = 'shopping'

class List
  include MongoMapper::Document
  key :name, String
  many :items
  
  def destroy_item!(item_id)
    items.delete_if do |i|
      i.id == item_id
    end    
    save
  end
end

class Item
  include MongoMapper::EmbeddedDocument
  key :price, Float 
end

# Setup prop
list = List.new({:name => 'groceries'})
cheap_item = Item.new({:price => 5.00})
expensive_item = Item.new({:price => 3.00})

list.items =  [] << cheap_item << expensive_item
list.save

puts "Is item count 2: #{list.items.count == 2}"

# Deletion by object id directly works fine
list.destroy_item!(expensive_item.id)
puts "Is item count 1: #{list.items.count == 1}"

# However if we send the object id as a string we get into trouble
list.destroy_item!(cheap_item.id.to_s)
puts "Is item count 0: #{list.items.count == 0}"

# This matters a fair bit when you are using restful resources over the web
# to handle the removal and updating of persisted objects.
#
# For example using sinatra we can handle a post to the
# resource /items/:list_id/:item_id/delete
#
# Rack then makes :item_id available in our params hash as a string, 
# and from there you can get easily caught out as in the example above.
#
# I don't mind working around this with my model code - it might not even be a bug 
# in mongo mapper bug perse. Just a bit assyemtric considering we can successfully 
# query for an object with find with the id represented as a string. The same
# should apply to equivalence tests on object ids.