Embedding message replies inside message parent wi

I think it's a best practice to embed replies to a specific message inside that message and I'm trying to implement it using mongoid. here is what I have

class Message
  include Mongoid::Document
  include Mongoid::Timestamps
  include Mongoid::Paranoia 

  field :subject
  field :body
  field :sender_deleted, :type => Boolean, :default => false
  field :recipient_deleted, :type => Boolean, :default => false
  field :read_at, :type => DateTime

  referenced_in :sender, :class_name => "User", :inverse_of => :sender, :foreign_key => 'sender_id'
  referenced_in :recipient, :class_name => "User", :inverse_of => :recipient, :foreign_key => 'recipient_id'

  embeds_many :replies, :class_name => 'Message'
  embedded_in :message, :inverse_of => :replies

here is the part where I try to define the message and its replies relation:

  embeds_many :replies, :class_name => 'Message'
  embedded_in :message, :inverse_of => :replies

it's not working for me and I don't know why, any idea how I can do such a thing?

Whether it is best practice or not is a highly debatable topic. For instance, you have to mind the object size limit (currently 4 MB, but will go up soon).

as for your question: I suggest that you change

  embeds_many :replies, :class_name => 'Message'
  embedded_in :message, :inverse_of => :replies

  embeds_many :replies, :class_name => 'Message'
  referenced_in :message

And you will also have to specify both connections manually (that should not be a problem, as they are probably immutable anyway).

irb(main):002:0> msg1 = Message.new :subject => 'new question'
=> #<Message _id: 4cc7699f457601d7e8000001, created_at: nil, body: nil, updated_at: nil, subject: "new question", read_at: nil, sender_deleted: false, message_id: nil, recipient_deleted: false>
irb(main):003:0> msg2 = Message.new :subject => 'first comment'
=> #<Message _id: 4cc769b6457601d7e8000002, created_at: nil, body: nil, updated_at: nil, subject: "first comment", read_at: nil, sender_deleted: false, message_id: nil, recipient_deleted: false>
irb(main):005:0> msg2.message = msg1
=> #<Message _id: 4cc7699f457601d7e8000001, created_at: nil, body: nil, updated_at: nil, subject: "new question", read_at: nil, sender_deleted: false, message_id: nil, recipient_deleted: false>
irb(main):007:0> msg1.replies << msg2
=> [#<Message _id: 4cc769b6457601d7e8000002, created_at: nil, body: nil, updated_at: nil, subject: "first comment", read_at: nil, sender_deleted: false, message_id: BSON::ObjectId('4cc7699f457601d7e8000001'), recipient_deleted: false>]
irb(main):008:0> msg1.save
=> true