belongs_to :note, :foreign_key => :note_id, :touch => true
belongs_to :author, :class_name => "User", :foreign_key => :author_id
validates :id, :uniqueness => true, :presence => { :on => :update },
belongs_to :note, :foreign_key => :note_id, :touch => true
belongs_to :author, :class_name => "User", :foreign_key => :author_id
validates :id, :uniqueness => true, :presence => { :on => :update },