widget_json_presenter.rb

require 'rubygems'
require 'active_support'
require 'active_support/core_ext/object/to_json.rb'
class Widget
  attr_accessor :id
  attr_accessor :name
  attr_accessor :gadgets
end

class Gadget
  attr_accessor :id
  attr_accessor :name
end

class GadgetPresenter
  attr_reader :id
  attr_reader :name
  def initialize(gadget)
    @id = %{gadget-#{gadget.id}}
    @name = gadget.name
  end
end

class WidgetPresenter
  attr_reader :id
  attr_reader :name
  attr_reader :children
  def initialize(widget)
    @id = %{widget-#{widget.id}}
    @name = widget.name
    @children = widget.gadgets.collect{|g| GadgetPresenter.new(g)}
  end
end

w = Widget.new
w.id = 47
w.name = 'name of widget'

g = Gadget.new
g.id = 63
g.name = 'name of gadget'

w.gadgets = [g]

p WidgetPresenter.new(w).to_json