Datamapper DataMapper

Hello,

I have been starting to experiment with DataMapper and have thus far been pretty pleased; unfortunately, I recently ran into a bug that is preventing me from continuing to use it in projects. When including dm-serializers and calling the "to_json" method on anything with included associations (via :methods), I get an exception thrown. (I will note that to_xml seems to work flawlessly.)

I have created the following illustrative use-case:

require 'rubygems'
require 'dm-core'
require 'dm-migrations'
require 'dm-serializer'

DataMapper.setup(:default, 'sqlite://:memory:')

class A
  include DataMapper::Resource
  property :id, Serial
  has n, :bs
end

class B
  include DataMapper::Resource
  property :id, Serial
  belongs_to :a
end

DataMapper.finalize
DataMapper.auto_migrate!

# Works fine, printing '[]'.
puts A.all.to_json(:methods => [:bs])

A.create

# Also works fine, printing '[{"id":1}]'.
puts A.all.to_json

# However, this one does not and throws an exception.
puts A.all.to_json(:methods => [:bs])

The output of executing this is as follows:

$ ruby -v
ruby 1.8.7 (2010-06-23 patchlevel 299) [x86_64-linux]
$ gem list
...
dm-core (1.0.0)
dm-migrations (1.0.0)
dm-serializer (1.0.0)
dm-sqlite-adapter (1.0.0)
...
$ ruby testcase.rb 
[]
[{"id":1}]
/usr/local/lib/ruby/gems/1.8/gems/dm-serializer-1.0.0/lib/dm-serializer/to_json.rb:76:in `to_json': undefined method `merge' for #<JSON::Ext::Generator::State:0x7fa00f0c7298> (NoMethodError)
    from /usr/local/lib/ruby/gems/1.8/gems/dm-serializer-1.0.0/lib/dm-serializer/to_json.rb:81:in `to_json'
    from testcase.rb:32

I would also note that using :methods is not well documented. The only place I found reference to it was on http://github.com/datamapper/dm-more/tree/master/dm-serializer#readme, in one little sentence under "How it works". Since I would imagine that serializing an object with associations to be a common use case (it certainly was in my case, building a JSON API with Sinatra and DataMapper), it would probably be wise to document this in more detail.