引用许多自身的模型？

Question

给定以下类，我如何允许节点与其他节点（例如 parent_node 和 child_nodes）具有多对多关系？

class Node
  include MongoMapper::Document

  key :text, String
end

Answer 1

孩子可以有多个父母吗？如果没有，many/belongs_to 应该可以正常工作：

class Node
  include MongoMapper::Document

  key :text, String
  key :parent_node_id, ObjectId

  belongs_to :parent_node, :class_name => 'Node'
  many :child_nodes, :foreign_key => :parent_node_id, :class_name => 'Node'
end

如果节点可以有多个父节点......

class Node
  include MongoMapper::Document

  key :text, String
  key :parent_node_ids, Array, :typecast => 'ObjectId'

  many :parent_nodes, :in => :parent_node_ids, :class_name => 'Node'

  # inverse of many :in is still forthcoming in MM
  def child_nodes
    Node.where(:parent_node_ids => self.id)
  end
end

# ... or store an array of child_node_ids instead ...

class Node
  include MongoMapper::Document

  key :text, String
  key :child_node_ids, Array, :typecast => 'ObjectId'

  many :child_nodes, :in => :child_node_ids, :class_name => 'Node'

  # inverse of many :in is still forthcoming in MM
  def parent_nodes
    Node.where(:child_node_ids => self.id)
  end
end

这就是您正在寻找的吗？