Mongoid example of using references_many with an embedded class

_explaination.txt

I found this challenging to figure out so I thought I would share:

This shows how you can establish a references_many relationship to an embedded class.  The limitation of course in my example is that when retrieving the ClientApplication's access_grants, it ends up retrieving User records.  I believe this is a limitation of MongoDB in that MongoDB can not retrieve just embedded objects.  It is not hard to accessing the embedded objects from the embedding class after retrieval. 

I access users like this:
@client_app.users

This is an example of the mongo query:
hub_test['users'].find({"access_grants.client_application_id"=>BSON::ObjectId('4d7fbead9ebea474c0000012')}, {})

Finding the access_grants requires an accessor method in ClientApplication:
@client_app.access_grants

access_grant.rb

class AccessGrant
  include Mongoid::Document
  embedded_in :user, :inverse_of => :access_grants
  referenced_in :client_application
end

client_application.rb

class ClientApplication
  require 'securerandom'
  include Mongoid::Document
  
  references_many :users,
                  :class_name => 'User',
                  :foreign_key => 'access_grants.client_application_id',
                  :inverse_of => :client_application
  
  def access_grants
    users.map { |u| u.access_grants.where(:client_application_id => id).all }.flatten
  end
end

user.rb

class User
  include Mongoid::Document
  embeds_many :access_grants
end