gem 'mongoid_denormalize'

$ gem install mongoid_denormalize

# Include the helper method
include Mongoid::Denormalize

# Define your denormalized fields
denormalize :name, :email, :from => :user

class User
  include Mongoid::Document
  include Mongoid::Denormalize

  has_many :comments
  has_many :moderated_comments, :class_name => "Comment", :inverse_of => :moderator

  field :name
  field :email
  
  denormalize :name, :email, :to => :comments
end

class Comment
  include Mongoid::Document
  include Mongoid::Denormalize

  belongs_to :user
  belongs_to :moderator, :class_name => "User", :inverse_of => :moderated_comments

  field :body
  
  denormalize :name, :email, :from => :user
end

>> user = User.create(:name => "John Doe", :email => "[email protected]")
>> comment = Comment.create(:body => "Lorem ipsum...", :user => user)
>> user.comments << comment
>> comment.user_name
"John Doe"
>> comment.user_email
"[email protected]"
>> user.update_attributes(:name => "Bill")
>> comment.user_name
"Bill"

# Basic denormalization. Will set the user_name attribute of "self.comments" to the value of "self.name".
denormalize :name, :to => :comments

# Multiple children. Will set the user_name attribute of "self.posts" and "self.comments" with "self.name".
denormalize :name, :to => [:posts, :comments]

# Basic denormalization, obeying :inverse_of. Will set the moderator_name attribute of "self.moderated_comments"
denormalize :name, :email, :to => :moderated_comments

# With custom field name prefix. Will set the commenter_name attribute of "self.comments" (takes precedence over
# inverse_of).
denormalize :name, :to => :comments, :as => :commenter

# Basic denormalization. Will set the user_name attribute with the associated user's name.
denormalize :name, :from => :user

# Multiple fields. Will set the user_name and user_email attributes with the associated user's name and email.
denormalize :name, :email, :from => :user

# Basic denormalization. Will set the moderator_name attribute with the associated author user's name.
denormalize :name, :from => :moderator

# in User
field :location, :type => Array
denormalize :location, :to => :posts

# in Post
denormalize :location, :type => Array, :from => :user

rake db:denormalize