Qu'il s'agisse de meilleures pratiques ou non est un sujet très discutable. Par exemple, vous devez tenir compte de la taille limite de l'objet (actuellement 4 Mo, mais qui augmentera bientôt).
en ce qui concerne votre question :je vous suggère de modifier
embeds_many :replies, :class_name => 'Message'
embedded_in :message, :inverse_of => :replies
à
embeds_many :replies, :class_name => 'Message'
referenced_in :message
Et vous devrez également spécifier les deux connexions manuellement (cela ne devrait pas poser de problème, car elles sont probablement immuables de toute façon).
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
