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 3.0 and later.

See, it's Rails 3 only.


The plugin is available as a gem:

gem 'nested_set'

Or install as a plugin:

rails plugin install git://


To make use of 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

  def self.down
    drop_table :categories

NB: There is no reason to use depth column. It's only add additional queries to DB without benefit. If you need level you should use each_with_level instead.

Enable the nested set functionality by declaring acts_as_nested_set on your model

class Category < ActiveRecord::Base

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

Conversion from other trees

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


Your tree be converted to a valid nested set.

View Helper

The view helper is called #nested_set_options.

Example usage:

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

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

or sorted select:

<%= :parent_id, sorted_nested_set_options(Category, lambda(&:name)) {|i, level| "#{'-' * level} #{}" } %>

<% sort_method = lambda{|x|} %>

NOTE: to sort UTF-8 strings you should use

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

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


bundle install

Running tests

bundle exec rake test

Benchmark tests

bundle exec ruby test/benchmark.rb


You can learn more about nested sets at:

1 2 3 4

How to contribute

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. Issues tracker
  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.
  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