PeopleAdmin fork¶ ↑

PeopleAdmin maintains a forked copy of AwesomeNestedSet.

The master branch will remain unchanged, so that it can be kept in synch with collectiveidea/awesome_nested_set.

Added features are maintained in separate branches, so that they can be submitted as pull requests independently. For example, the subset branch contains all changes related to our proposed :subset option.

Our Gemfile will refer to this deploy branch. All changes from master and our feature branches should be merged into deploy. No changes should be made directly to the deploy branch (other than the merge commits, and this Readme.rdoc).

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