Tree example in MongoMapper

Node.rb

class Node
  include MongoMapper::Document
  key :name
  belongs_to :parent, :class_name => 'Node'
  many :children, :class_name => 'Node'

  def root?
    parent.nil?
  end

  def branch?
    children.each {|c| return true if c.leaf? }
    false
  end
  
  def leaf?
    self.children.empty?
  end
  
  def depth(d=1)
    depth = d
    depth += parent.depth(d) if parent
    depth
  end
  
  def to_s(starting_here=true)
    text = name
    starting_depth = self.depth
    starting_depth = 1 if starting_here
    children.each do |c| 
      depth = c.depth(starting_depth)
      spacer = " "*depth
      text += "\n#{spacer}#{c.to_s(false)}"
    end
    text
  end
  
  def self.show_all
    Node.where(:parent_id => nil).sort(:created_at).all.each do |n|
      puts n
    end
  end
  
end

=begin  
 animals
   fish
   mammals
 extinct
 region
   asia
     japan
     china
   europe
     france
=end

Node.destroy_all
root = Node.create(:name => "root")
    animals = Node.create( :name => "animals", :parent => root )
        fish    = Node.create(:name => "fish", :parent => animals)
        mammals = Node.create(:name => "mammals", :parent => animals)
            horse = Node.create(:name => "horse", :parent => mammals)
            dog = Node.create(:name => "dog", :parent => mammals)
            human = Node.create(:name => "human", :parent => mammals)
        mammals.children << [horse, dog, human]
        mammals.save!
    animals.children << [fish, mammals]
    animals.save!
    reptiles = Node.create(:name => "reptiles", :parent => root)
    extinct  = Node.create( :name => "extinct", :parent => root )
    region   = Node.create( :name => "region", :parent => root )
        asia = Node.create( :name => "asia", :parent => region )
            japan = Node.create(:name => "japan", :parent => asia)
            china = Node.create(:name => "china", :parent => asia)
        asia.children << [japan, china]
        asia.save!
    region.children << asia
    region.save!
root.children << [animals, reptiles, extinct, region]
root.save!

Node.show_all

sample_output.txt

If you dump the above "code" into mmconsole, you should get something like this:

    ruby-1.9.2-p180 :2651 >   Node.show_all
    root
      extinct
      animals
          fish
          mammals
                human
                horse
                dog
      reptiles
      region
          asia
                japan
                china