gistfile1.rb

class Node < ActiveRecord::Base
  attr_accessor :related_nodes_ids

  after_save :save_related_nodes 
  before_destroy :clear_related_nodes

  def related_nodes=(nodes_ids)
    @related_nodes_ids = nodes_ids.compact.reject { |s| s.blank? }
  end

  def related_nodes
    self.id.nil? ? [] : Node.joins('LEFT OUTER JOIN related_nodes ON related_nodes.related_node_id = nodes.id').where('related_nodes.node_id' => self.id)    
  end

  def save_related_nodes
    return if @related_nodes_ids.nil?
    clear_related_nodes
    @related_nodes_ids.each do |related_node_id|
      RelatedNode.create!(:node_id => self.id, :related_node_id => related_node_id)
    end
  end

  def clear_related_nodes
    RelatedNode.delete_all(:node_id => self.id)
  end

end