followers association with mongoid twitter style

followers association with mongoid twitter style

What is the best way to model user/follower (twitter style) relationships with mongo? Most prominent solution is to embed an array of followers ids in every user object. I'm an idealist, and believe that if we are modeling twitter, we eventually will run into a situation when a user has millions of followers which will blow. The relational many_to_many is not easy to model with mongo, mongo_id tries to offer some implementation of basic associations, but the many_no_many, or has_many through is not there yet and I doubt it ever will be. 
My solution is a compromise between relational normalization and "embed everything in one document".


class User
  include Mongoid::Document
  include Mongoid::Timestamps

  # user will have many followerships, each will embedd a follower user, 
  # the user_id is stored on the followership object
  references_many :followerships
end

class Followership
  include Mongoid::Document
  include Mongoid::Timestamps
  # the user_id is stored on this object, which defines the parent user object which is being followed
  referenced_in :user
  # embedded user object is a follower
  embeds_one :follower, :class_name=>"User"
end

Not really, it was all theoretical, and it was never really put in prod.