awesome nested set for rails 3 using mongomapper

i want to use awesome nested set for rails 3 using mongomapper in my app. i have seen mongo nested set gem and added it to my gemfile and bundle install.

Then i add acts_as_nested_set to my mongomapper model and i get error :

NameError: undefined local variable or method `acts_as_nested_set' 

Is this for rails 3 ? Am i missing something to include this gem into my model or something ?

Or does anyone know of a better solution for mongomappe开发者_开发问答r ?

EDIT : Got this error fixed by including the MongoNestedSet like this :

class Category

  include MongoMapper::Document

  include MongoNestedSet

    acts_as_nested_set

        key :name, String, :required => true
    key :parent_id, String
    key :lft, Integer
    key :rgt, Integer

end

but now when i try Category.create!(:name => 'Science') i get the following error :

NoMethodError: undefined method `rgt' for []:Array
    from /Users/aaaa/.rvm/gems/ruby-1.9.2-p180/gems/mongo_nested_set-0.1.1/lib/mongo_nested_set.rb:440:in `set_default_left_and_right'

Any one please help with this ?

thanks rick

I am new to rails and I had a similar problem with acts_as_nested_set

I just edited the Gemfile and added the following line:

gem 'awesome_nested_set'

The error message disappeared!