Given the following models

class House
include Mongoid::Document
field :stories, :type => Integer, :default => 1
embeds_many :rooms
end

class Room
include Mongoid::Document
field :doors, :type => Integer, :default => 1
embedded_in :house, :inverse_of :rooms
end

And given the following documents

Mongoid.database[:houses].insert({})
Mongoid.database[:houses].insert({ 'stories' => nil, 'rooms' => [{}] })

Then I would expect

>> House.first.stories #=> 1
>> House.first.rooms #=> []
>> House.last.stories #=> nil
>> House.last.rooms.first.doors #=> 1

Instead the result is the following

>> House.first.stories #=> nil
>> House.first.rooms #=> []
>> House.last.rooms.first.doors #=> nil

This allows Mongoid to support the following features offered by column defaults in relational databases and mirror ActiveRecord capabilities:

• Defaults are retroactive to records predating the field
• Any change to the default applies to any record that has not had the field explicitly set