別のクラスで同じクラスを複数回参照するにはどうすればよいですか？

Question

Mongoidで同じクラスを別のクラスで2回（または複数回）参照するにはどうすればよいですか？

class User 
    include Mongoid::Document 
    field :email 

    references_many :messages, :stored_as => :array #all messages where the user acts as a sender 
    references_many :messages, :stored_as => :array #all messages where the user acts as a receiver 
end 

class Message 
    include Mongoid::Document 
    field :Text 

    references_one :user #this should be the sender 
    references_one :user #this should be the receiver 
end 

Answer 1

references_many：sent_messages：stored_as =>：配列：CLASS_NAME => 'メッセージ'

と

references_one：送信者：CLASS_NAME => 'ユーザ'