+ # using belongs_to :foreign_key = 'node_*', since if use has_one :foreign_key = 'id', segment preconditions? fails checking for segment id in node table
+ belongs_to :from_node, :class_name => 'Node', :foreign_key => 'node_a'
+ belongs_to :to_node, :class_name => 'Node', :foreign_key => 'node_b'