Idea for lazily loading attributes in MM

irb.rb

>> user = User..first
=> …
>> user.collaborators_loaded?
=> false
>> user.collaborators.size          # <= loads all lazy fields
=> 30
>> user.collaborators_loaded?
=> true
>> user.time_zone_loaded?
=> true

# Using #fields overrides lazy settings
>> user = User.fields(:name).first
=> …
>> user.email_loaded?
=> false
>> user.email                       # <= loads lazy fields
=> "brandon@example.com"
>> user.email_loaded?
=> true
>> user.collaborators_loaded?
=> true

models.rb

class User
  include MongoMapper::Document
  
  key :name
  key :email
  key :time_zone,       :lazy => true

  many :collaborators,  :lazy => true
end

class Collaborator
  include MongoMapper::EmbeddedDocument
  
  timestamps!
  belongs_to :user
end