embed_many.rb

class UserAccountsController < ApplicationController
  def signin
    auth = request.env['rack.auth']
    
    user_for_provider_and_uid  = UserAccount.find_by_provider_and_uid(auth['provider'], auth['uid']).first()
    new_auth = Authorization.new(:user_id => auth['user_id'], :provider => auth['provider'], :uid => auth['uid'], :user_info => auth['user_info'], :credentials => auth['credentials'])

    if user_for_provider_and_uid.nil?
      user = signed_in? ? self.current_user : UserAccount.new(:name => auth['user_info']['name'])
      user.authorizations << new_auth
      user.save!
      self.current_user = user
    else
      self.current_user = user_for_provider_and_uid
    end

    redirect_to :root
  end
end



class UserAccount
  include Mongoid::Document
   field :name, :type => String
   field :admin, :type => Boolean, :default => false
   
   references_many :lists, :stored_as => :array, :inverse_of => :users
   embeds_many :authorizations, :class_name => "Authorization"
    
   def self.find_by_provider_and_uid(provider, uid)
      UserAccount.where("authorizations.provider" => provider).and("authorizations.uid" => uid)
   end
end

class Authorization 
  include Mongoid::Document
  field :provider, :type => String
  field :uid, :type => String 
  field :user_id, :type => Integer
  field :user_info, :type => Hash
  field :user_credentials, :type => Hash

  embedded_in :useraccount, :inverse_of => :authorizations # Remove this and it starts behaving badly!
end