# A top level document in the account collection
class Account
  include Mongoid::Document

  has_many :projects, :dependent => :destroy

  after_destroy do
    puts "After destroy account fired"
  end
end

# A top level document in the project collection
class Project
  include Mongoid::Document

  belongs_to :account

  after_destroy do
    puts "After destroy project fired"
  end
end

# A top level document in the invoice collection
class Invoice
  include Mongoid::Document

  embeds_one :plan, :cascade_callbacks => true
end

# An embedded document, that no collection exists for
class Plan
  include Mongoid::Document

  embedded_in :invoice
end

account = Account.create
Project.create! account: account
invoice = account.invoices.new

# We shouldn't be allowed to set an Account to a Plan here, it's not a Plan class
invoice.plan = a
invoice.save!

# Here the account will have its after_destory callbacks fired and the projects destroyed...
invoice.plan = nil