belongs_to :old_node, :foreign_key => [:node_id, :version]
- validates :old_node, :presence => true, :associated => true
+ validates :old_node, :associated => true
validates :k, :v, :allow_blank => true, :length => { :maximum => 255 }, :characters => true
validates :k, :uniqueness => { :scope => [:node_id, :version] }
end