这是可行的，但我强烈建议使用 has_many :through 代替:

This is doable, but I strongly recommend using has_many :through instead:

class Node < ActiveRecord::Base
  has_many :parent_node_links,
    :class_name => 'NodeLink',
    :foreign_key => :child_id

  has_many :parents,
    :through => :parent_node_links,
    :source => :parent

  has_many :child_node_links,
    :class_name => 'NodeLink',
    :foreign_key => :parent_id

  has_many :children,
    :through => :child_node_links,
    :source => :child
end

class NodeLink < ActiveRecord::Base
  belongs_to :parent,
    :class_name => "Node"
  belongs_to :child,
    :class_name => "Node"
end

拥有一流的连接模型可以更轻松地管理关系，并让您可以在以后***添加相关元数据.

Having a first-class join model makes it much easier to manage the relationships and gives you the freedom to add relevant meta-data at a later point in time.