Mongoid references_many adding problem

mongoid_add_to_references_many_relation_test.rb

require 'mongoid'
require 'test/unit'

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

class Node
  include Mongoid::Document
  
  field :title, :type => String
  
  references_many :children, :class_name => "Node",
                             :foreign_key => :parent_id
                             
  referenced_in :parent, :class_name => "Node"
end

class AddingToReferencesManyTest < Test::Unit::TestCase
  n1 = Node.create :title => "Node 1"
  n2 = Node.create :title => "Node 2"
  n1.children << n2
  n1.save
  assert_equal [n2], n1.reload.children
end

output

10:49 ~/Code>gem which mongoid
/Users/jeremyweiland/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/mongoid.rb
10:49 ~/Code>ruby -v
ruby 1.9.2p180 (2011-02-18 revision 30909) [x86_64-darwin10.7.0]
10:49 ~/Code>ruby mongoid_test.rb
/Users/jeremyweiland/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/mongoid/attributes.rb:162:in `method_missing': undefined method `entries' for #<Node:0x000001010e27a0> (NoMethodError)
        from /Users/jeremyweiland/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/mongoid/relations/referenced/many.rb:219:in `block in load!'
        from /Users/jeremyweiland/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/mongoid/relations/referenced/many.rb:217:in `tap'
        from /Users/jeremyweiland/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/mongoid/relations/referenced/many.rb:217:in `load!'
        from /Users/jeremyweiland/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/mongoid/relations/accessors.rb:28:in `block in build'
        from /Users/jeremyweiland/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/mongoid/relations/accessors.rb:27:in `tap'
        from /Users/jeremyweiland/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/mongoid/relations/accessors.rb:27:in `build'
        from /Users/jeremyweiland/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/mongoid/relations/accessors.rb:166:in `block (2 levels) in setter'
        from /Users/jeremyweiland/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/mongoid/extensions/object/yoda.rb:22:in `do_or_do_not'
        from /Users/jeremyweiland/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/mongoid/relations/bindings/referenced/many.rb:46:in `bind_one'
        from /Users/jeremyweiland/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/mongoid/relations/referenced/many.rb:299:in `append'
        from /Users/jeremyweiland/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/mongoid/relations/referenced/many.rb:29:in `block (2 levels) in <<'
        from /Users/jeremyweiland/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/mongoid/relations/referenced/many.rb:27:in `each'
        from /Users/jeremyweiland/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/mongoid/relations/referenced/many.rb:27:in `block in <<'
        from /Users/jeremyweiland/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/mongoid/relations/referenced/batch.rb:64:in `count_executions'
        from /Users/jeremyweiland/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/mongoid/relations/referenced/batch.rb:40:in `batched'
        from /Users/jeremyweiland/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/mongoid/relations/referenced/many.rb:26:in `<<'
        from mongoid_test.rb:22:in `<class:AddingToReferencesManyTest>'
        from mongoid_test.rb:19:in `<main>'

I think you are just missing the inverse_of. See below

class Node
  include Mongoid::Document

  field :title, :type => String

  references_many :children, :class_name => "Node",
                             :foreign_key => :parent_id, :inverse_of => :parent

  referenced_in :parent, :class_name => "Node"
end

I updated the example to reflect the relations in my production app.