AwesomeNestedSet

Awesome Nested Set is an implementation of the nested set pattern for ActiveRecord models. It is a 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:

ruby gem 'awesome_nested_set'

Usage

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

```ruby 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

ruby class Category < ActiveRecord::Base acts_as_nested_set end

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

Callbacks

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

```ruby 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.

```ruby 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 “whitelist” the attributes that can be used in mass assignment:

ruby 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:

ruby 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:

ruby 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:

```erb <%= f.select :parent_id, nested_set_options(Category, @category) {|i| “#{‘-‘ * i.level} #ii.name” } %>

<%= select_tag ‘parent_id’, options_for_select(nested_set_options(Category) {|i| “#{‘-‘ * i.level} #ii.name” } ) %> ```

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

References

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

How to contribute

Please see the ‘Contributing’ document.