Mongoid HABTM Issue

left.rb

class Left
  include Mongoid::Document

  field :title, :type => String
  has_and_belongs_to_many :rights
end

main.rb

require 'rubygems'
require 'mongoid'

Mongoid.configure do |config|
  config.master = Mongo::Connection.new.db("habtm_test")
end

puts 'Empty our database.'
Mongoid.master.collections.reject { |c| c.name =~ /^system/}.each(&:drop)

require 'left'
require 'right'

puts 'Create a left and a right object.'
left = Left.create!(:title => 'Left Test')
right = Right.create!(:title => 'Right Test')

puts "Find first left: #{Left.first.inspect}"
puts "Find first right: #{Right.first.inspect}"

puts 'Associated them to each other.'
left.rights << right

puts "Rights associated with lefts: #{left.rights.inspect}"
puts "Lefts associated with rights: #{right.lefts.inspect}"

puts 'Clear the association collection.'
left.rights.clear

puts "Rights associated with lefts: #{left.rights.inspect}"
puts "Lefts associated with rights: #{right.lefts.inspect}"

puts 'Retrieve the first left and first right object from the database.'
puts "Find first left: #{Left.first.inspect}"
puts "Find first right: #{Right.first.inspect}" # We no longer have our right object!

puts '** Notice that "Right.first.inspect" returns nil. It was deleted when we cleared the habtm collection.\n\n'


puts "Let's associate them again, but this time set the collection to [] instead of using clear."

puts "Create a new right object."
right = Right.create!(:title => 'Right Test')

puts 'Associated them to each other.'
left.rights << right

puts "Rights associated with lefts: #{left.rights.inspect}"
puts "Lefts associated with rights: #{right.lefts.inspect}"

puts 'Set the collection to an empty array [].'
left.rights = []

puts "Rights associated with lefts: #{left.rights.inspect}"
puts "Lefts associated with rights: #{right.lefts.inspect}"

puts 'Retrieve the first left and first right object from the database.'
puts "Find first left: #{Left.first.inspect}"
puts "Find first right: #{Right.first.inspect}" # We no longer have our right object!

puts '** Notice that this time the right object was NOT deleted, but the associations were properly cleared using the = syntax.'

right.rb

class Right
  include Mongoid::Document

  field :title, :type => String
  has_and_belongs_to_many :lefts
end