gistfile1.rb

class Quiz
  include Mongoid::Document
  embeds_many :topics

  # fields...
end

class Topic
  include Mongoid::Document
  embedded_in :quiz
end

quiz = Fabricate :quiz
 => #<Quiz _id: 4d2ac0cf0de0691cb5000666, created_at: 2011-01-10 08:18:23 UTC, updated_at: 2011-01-10 08:18:23 UTC, user_id: BSON::ObjectId('4d2ac0cf0de0691cb5000667'), time: 0, number: 1, built_at: nil, completed_at: nil, graded_at: nil> 
quiz.attributes
 => {"time"=>0, "_id"=>BSON::ObjectId('4d2ac0cf0de0691cb5000666'), "user_id"=>BSON::ObjectId('4d2ac0cf0de0691cb5000667'), "created_at"=>2011-01-10 08:18:23 UTC, "number"=>1, "updated_at"=>2011-01-10 08:18:23 UTC, "topics"=>[{"_id"=>1}, {"_id"=>3}]} 
quiz.topics
 => [#<Topic _id: 1, score: nil, given: nil, correct: nil>, #<Topic _id: 3, score: nil, given: nil, correct: nil>] 
quiz.topics = [Topic.new(:_id => 2)]
 => [#<Topic _id: 2, score: nil, given: nil, correct: nil>] 
quiz.topics
 => [#<Topic _id: 2, score: nil, given: nil, correct: nil>] 
quiz.attributes
 => {"time"=>0, "_id"=>BSON::ObjectId('4d2ac0cf0de0691cb5000666'), "user_id"=>BSON::ObjectId('4d2ac0cf0de0691cb5000667'), "created_at"=>2011-01-10 08:18:23 UTC, "number"=>1, "updated_at"=>2011-01-10 08:18:23 UTC, "topics"=>[{"_id"=>1}, {"_id"=>3}]} 
quiz.save
 => true 
quiz.attributes
 => {"time"=>0, "_id"=>BSON::ObjectId('4d2ac0cf0de0691cb5000666'), "user_id"=>BSON::ObjectId('4d2ac0cf0de0691cb5000667'), "created_at"=>2011-01-10 08:18:23 UTC, "number"=>1, "updated_at"=>2011-01-10 08:19:42 UTC, "topics"=>[{"_id"=>1}, {"_id"=>3}]} 
quiz.reload
 => #<Quiz _id: 4d2ac0cf0de0691cb5000666, created_at: 2011-01-10 08:18:23 UTC, updated_at: 2011-01-10 08:19:42 UTC, user_id: BSON::ObjectId('4d2ac0cf0de0691cb5000667'), time: 0, number: 1, built_at: nil, completed_at: nil, graded_at: nil> 
quiz.attributes
 => {"_id"=>BSON::ObjectId('4d2ac0cf0de0691cb5000666'), "created_at"=>2011-01-10 08:18:23 UTC, "number"=>1, "time"=>0, "topics"=>[{"_id"=>2}], "updated_at"=>2011-01-10 08:19:42 UTC, "user_id"=>BSON::ObjectId('4d2ac0cf0de0691cb5000667')}