Acts As Ordered Tree

WARNING! THIS GEM IS NOT COMPATIBLE WITH ordered_tree gem.

Specify this acts_as extension if you want to model an ordered tree structure (adjacency list hierarchical structure) by providing a parent association, a children association and a sort column. For proper use you should have a foreign key column, which by default is called parent_id, and a sort column, which is by default called position. Comparison of Adjacency List model to others: http://vadimtropashko.wordpress.com/2008/08/09/one-more-nested-intervals-vs-adjacency-list-comparison/

This extension is mostly compatible with awesome_nested_set gem

Requirements

Gem is supposed to work with Rails 3.1 and higher including newest Rails 4.2. We test it with ruby-1.9.3, ruby-2.0.0, ruby-2.1.0 and jruby-1.7.8. Sorry, support for ruby 1.9.2 and 1.8.7 is dropped. Also, rubunius isn't supported since it's quite unstable (I could not even launch rails 3.2 with rbx-2.1.1).

Features

1. Supports PostgreSQL recursive queries (requires at least postgresql-8.3)
2. Holds integrity control via pessimistic database locks. Common situation for acts_as_list users is non-unique positions within list. It happens when two concurrent users modify list sumultaneously. acts_as_ordered_tree uses pessimistic locks to keep your tree consistent.

Installation

Install it via rubygems:

gem install acts_as_ordered_tree

Usage

To make use of acts_as_ordered_tree, your model needs to have 2 fields: parent_id and position. You can also have an optional fields: depth and children_count:

class CreateCategories < ActiveRecord::Migration
  def self.up
    create_table :categories do |t|
      t.integer :company_id
      t.string  :name
      t.integer :parent_id # this is mandatory
      t.integer :position # this is mandatory
      t.integer :depth # this is optional
      t.integer :children_count # this is optional
    end
  end

  def self.down
    drop_table :categories
  end
end

Setup your model:

class Category < ActiveRecord::Base
  acts_as_ordered_tree

  # gem introduces new ActiveRecord callbacks:
  # *_reorder - fires when position (but not parent node) is changed
  # *_move - fires when parent node is changed
  before_reorder :do_smth
  before_move :do_smth_else
end

Now you can use acts_as_ordered_tree features:

# root
#  \_ child1
#       \_ subchild1
#       \_ subchild2


root = Category.create(:name => "root")
child1 = root.children.create(:name => "child1")
subchild1 = child1.children.create("name" => "subchild1")
subchild2 = child1.children.create("name" => "subchild2")

Category.roots # => [root]

root.root? # => true
root.parent # => nil
root.ancestors # => []
root.descendants # => [child1, subchild1, subchild2]
root.descendants.arrange # => {child1 => {subchild1 => {}, subchild2 => {}}}
# you may pass an option to discard possible orphans from selection
root.descendants.arrange(:orphans => :discard)

child1.parent # => root
child1.ancestors # => [root]
child1.children # => [subchild1, subchild2]
child1.descendants # => [subchild1, subchild2]
child1.root? # => false
child1.leaf? # => false

subchild1.ancestors # => [child1, root]
subchild1.root # => [root]
subchild1.leaf? # => true
subchild1.first? # => true
subchild1.last? # => false
subchild2.last? # => true

subchild1.move_to_above_of(child1)
subchild1.move_to_bottom_of(child1)
subchild1.move_to_child_of(root)
subchild1.move_lower
subchild1.move_higher

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Added some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request

TODO

1. Fix README typos and grammatical errors (english speaking contributors are welcomed)
2. Add moar examples and docs.
3. Implement converter from other structures (nested_set, closure_tree)