rails many to many relationship same model
class Page < ActiveRecord::Base
has_many :left_page_associations, :foreign_key => :left_page_id,
:class_name => 'PageAssociation'
has_many :left_associations, :through => :left_page_associations,
:source => :right_page
has_many :right_page_associations, :foreign_key => :right_page_id,
:class_name => 'PageAssociation'
has_many :right_associations, :through => :right_page_associations,
:source => :left_page
end