attr_accessor_mongoid_1.rb

require 'rubygems'
puts ENV["GEM_HOME"]
require 'mongoid'
require 'mongoid/version'

puts "Using Mongoid: #{Mongoid::VERSION}"

Mongoid.master = Mongo::Connection.new.db("mongoid_playground")

class Orphan
 include Mongoid::Document

 attr_accessor :mode
 field :name, :type => String

 embedded_in :parent, :inverse_of => :orphans


 def loud_speak
  puts "HOLLLLLLLA! #{self.name}"
 end

 def soft_speak
  puts "holla. #{self.name}"
 end

 def speak
  puts "mode = #{self.mode}"    #mode doesn't exist
  #eval "#{@mode}_speak" 
  soft_speak
 end 

end

class Parent
 include Mongoid::Document
 cache
 field :name, :type => String

 embeds_many :orphans
end

class Child < Parent
end

Parent.delete_all
Child.delete_all

p = Parent.new(:title => "parent1")
o = Orphan.new(:name => "Annie")

p.orphans << o
p.save

results = Parent.all
results.each{ |r| r.orphans.first.mode = "loud" }

results.each{ |r| r.orphans.first.speak }

I added cache to parent on line 37 to show you how to resolve it... attr_accessor works fine - you were doing a second iteration over the result set which was hitting the database again (unlike active record which brings everything into memory). Mongoid uses a cursor so if you didnt want to do that on iteration 2 you cache the class in this case.

See the caching section: http://mongoid.org/docs/extras/

If you had printed out "mode" in the first iteration you would have seen it get set.