Awesome Nested Set is an implementation of the nested set pattern for ActiveRecord models. It is replacement for acts_as_nested_set and BetterNestedSet, but awesomer. It supports Rails 2.1 and later.

This is a new implementation of nested set based off of BetterNestedSet that fixes some bugs, removes tons of duplication, adds a few useful methods, and adds STI support.

Install as a plugin:

rails plugin install git://github.com/galetahub/awesome_nested_set.git

as a gem:

gem 'awesome_nested_set', :git => 'git://github.com/galetahub/awesome_nested_set.git'

To make use of awesome_nested_set, your model needs to have 3 fields: lft, rgt, and parent_id:

class CreateCategories < ActiveRecord::Migration
  def self.up
    create_table :categories do |t|
      t.string :name
      t.integer :parent_id
      t.integer :lft
      t.integer :rgt

      # Uncomment it to store item level
      # t.integer :depth
    end
  end

  def self.down
    drop_table :categories
  end
end

Enable the nested set functionality by declaring acts_as_nested_set on your model

class Category < ActiveRecord::Base
  acts_as_nested_set
end

Run ‘rake rdoc` to generate the API docs and see CollectiveIdea::Acts::NestedSet::Base::SingletonMethods for more info.

Coming from acts_as_tree or another system where you only have a parent_id? No problem. Simply add the lft & rgt fields as above, and then run

Category.rebuild!

Your tree be converted to a valid nested set. Awesome!

The view helper is called #nested_set_options.

Example usage:

<%= f.select :parent_id, nested_set_options(Category, @category) {|i| "#{'-' * i.level} #{i.name}" } %>

<%= select_tag 'parent_id', options_for_select(nested_set_options(Category) {|i| "#{'-' * i.level} #{i.name}" } ) %>

See CollectiveIdea::Acts::NestedSet::Helper for more information about the helpers.

You can learn more about nested sets at:

http://www.dbmsmag.com/9603d06.html
http://threebit.net/tutorials/nestedset/tutorial1.html
http://api.rubyonrails.com/classes/ActiveRecord/Acts/NestedSet/ClassMethods.html
http://opensource.symetrie.com/trac/better_nested_set/

If you find what you might think is a bug:

1. Check the GitHub issue tracker to see if anyone else has had the same issue. github.com/collectiveidea/awesome_nested_set/issues/

2. If you don’t see anything, create an issue with information on how to reproduce it.

If you want to contribute an enhancement or a fix:

1. Fork the project on github. github.com/collectiveidea/awesome_nested_set/

2. Make your changes with tests.

3. Commit the changes without making changes to the Rakefile, VERSION, or any other files that aren’t related to your enhancement or fix

4. Send a pull request.

Copyright ©2010 Collective Idea, released under the MIT license