class Bundle
  embeds_many :items
end

class Item
  embedded_in :bundle
end

bundle = Bundle.new(items: Item.new)
bundle.persisted? # => false
bundle.items.first.persisted? # => false
bundle.items = [] 

 
def embedded_atomic_selector
  if persisted? && _id_changed?
    _parent.atomic_selector
  else
     binding.pry
     _parent.atomic_selector.merge("#{atomic_path}._id" => _id)
  end
end

_parent # => nil