redmine/lib/plugins/acts_as_tree/README

acts_as_tree
============

Specify this +acts_as+ extension if you want to model a tree structure by providing a parent association and a children
association. This requires that you have a foreign key column, which by default is called +parent_id+.

  class Category < ApplicationRecord
    acts_as_tree :order => "name"
  end

  Example:
  root
   \_ child1
        \_ subchild1
        \_ subchild2

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

  root.parent   # => nil
  child1.parent # => root
  root.children # => [child1]
  root.children.first.children.first # => subchild1

Copyright (c) 2007 David Heinemeier Hansson, released under the MIT license