AwesomeNestedSet¶ ↑

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 more awesome.

Version 2 supports Rails 3. Gem versions prior to 2.0 support Rails 2.

What makes this so awesome?¶ ↑

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.

Installation¶ ↑

Add to your Gemfile:

gem 'awesome_nested_set'

Usage¶ ↑

To make use of awesome_nested_set, your model needs to have 3 fields: lft, rgt, and parent_id. You can also have an optional field: depth:

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
      t.integer :depth # this is optional.
    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 for more info.

Callbacks¶ ↑

There are three callbacks called when moving a node. ‘before_move`, `after_move` and `around_move`.

class Category < ActiveRecord::Base
  acts_as_nested_set

  after_move :rebuild_slug
  around_move :da_fancy_things_around

  private

  def rebuild_slug
    # do whatever
  end

  def da_fancy_things_around
    # do something...
    yield # actually moves
    # do something else...
  end
end

Beside this there are also hooks to act on the newly added or removed children.

class Category < ActiveRecord::Base  
  acts_as_nested_set  :before_add     => :do_before_add_stuff,
                      :after_add      => :do_after_add_stuff,
                      :before_remove  => :do_before_remove_stuff,
                      :after_remove   => :do_after_remove_stuff

  private

  def do_before_add_stuff(child_node)
    # do whatever with the child
  end

  def do_after_add_stuff(child_node)
    # do whatever with the child
  end

  def do_before_remove_stuff(child_node)
    # do whatever with the child
  end

  def do_after_remove_stuff(child_node)
    # do whatever with the child
  end
end

Protecting attributes from mass assignment¶ ↑

It’s generally best to “white list” the attributes that can be used in mass assignment:

class Category < ActiveRecord::Base
  acts_as_nested_set
  attr_accessible :name, :parent_id
end

If for some reason that is not possible, you will probably want to protect the lft and rgt attributes:

class Category < ActiveRecord::Base
  acts_as_nested_set
  attr_protected :lft, :rgt
end

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

Category.rebuild!

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

View Helper¶ ↑

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.

References¶ ↑

You can learn more about nested sets at: threebit.net/tutorials/nestedset/tutorial1.html

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. 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 ©2008 Collective Idea, released under the MIT license