= ActsAsOrderedTree
  v.1.2
                                 +----+-----------+----------+---------+
  node_1                         | id | parent_id | position | name    |
    \_ node_2                    +----+-----------+----------+---------+
    \_ node_3                    |  1 |         0 |        1 | Node_1  |
    |    \_ node_4               |  2 |         1 |        1 | Node_2  |
    |    \_ node_5               |  3 |         1 |        2 | Node_3  |
    |    |   \_ node_8           |  4 |         3 |        1 | Node_4  |
    |    |   \_ node_9           |  5 |         3 |        2 | Node_5  |
    |    \_ node_10              |  6 |         1 |        3 | Node_6  |
    |    \_ node_11              |  7 |         1 |        4 | Node_7  |
    \_ node_6                    |  8 |         5 |        1 | Node_8  |
    \_ node_7                    |  9 |         5 |        2 | Node_9  |
    |                            | 10 |         3 |        3 | Node_10 |
    |                            | 11 |         3 |        4 | Node_11 |
  node_12                        | 12 |         0 |        2 | Node_12 |
    \_ node_13                   | 13 |        12 |        1 | Node_13 |
    \_ node_14                   | 14 |        12 |        2 | Node_14 |
    |    \_ node_15              | 15 |        14 |        1 | Node_15 |
    |    \_ node_16              | 16 |        14 |        2 | Node_16 |
    |    |   \_ node_19          | 17 |        12 |        3 | Node_17 |
    |    |   \_ node_20          | 18 |        12 |        4 | Node_18 |
    |    \_ node_21              | 19 |        16 |        1 | Node_19 |
    |    \_ node_22              | 20 |        16 |        2 | Node_20 |
    \_ node_17                   | 21 |        14 |        3 | Node_21 |
    \_ node_18                   | 22 |        14 |        4 | Node_22 |
                                 +----+-----------+----------+---------+


  class Person < ActiveRecord::Base
    acts_as_ordered_tree :foreign_key => :parent_id,
                         :order       => :position
  end

  class CreatePeople < ActiveRecord::Migration
    def self.up
      create_table :people do |t|
        t.column :parent_id ,:integer ,:null => false ,:default => 0
        t.column :position  ,:integer
      end
      add_index(:people, :parent_id)
    end
  end

  Which "in effect" sets up the following:

      belongs_to :parent,
                 :class_name  => Person,
                 :foreign_key => :parent_id

      has_many   :children,
                 :class_name  => Person,
                 :foreign_key => :parent_id,
                 :order       => :position



= Overview

     Actions    Tree Methods                                List Method
 --------------------------------------------------------------------------------------------------
     Create
                To create a child object at a specific position,
                use one of the following:
                  Person.create(:parent_id => parent.id, :position => 2)
                  parent.children << Person.new(:position => 3)
                  parent.children.create(:position => 5)

                To create a new 'root', use:
                  Person.create(:position => 2)

                :position will default to the bottom of the parent's list
                :parent_id defaults to 0 (Class.roots)

     Read
                roots (class method)                        self_and_siblings

                root                                        siblings

                parent                                      position_in_list

                ancestors

                children

                descendants

     Update
                shift_to(parent = nil, position = nil)      move_above(sibling = nil)

                orphan                                      move_higher

                orphan_children                             move_lower

                parent_adopts_children                      move_to_top

                orphan_self_and_children                    move_to_bottom

                orphan_self_and_parent_adopts_children

     Destroy
                destroy (deletes all descendants)

                destroy_and_orphan_children

                destroy_and_parent_adopts_children

= Install

  ./script/plugin install svn://rubyforge.org/var/svn/ordered-tree/acts_as_ordered_tree

  To test, run 'rake test:plugins', or 'rake' from the plugin's directory.

  There is a drag-n-drop demo located at svn://rubyforge.org/var/svn/ordered-tree/demo

= License

Copyright (c) 2006,2007 Brian D. Burns <[email protected]>

Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the "Software"), to deal in
the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
the Software, and to permit persons to whom the Software is furnished to do so,
subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.