Redmine/lib/plugins/awesome_nested_set

= 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: http://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.
   https://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.
   https://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