class Parent
  include Mongoid::Document
  include AASM

  field :status, :type => String
  has_many :childs

  aasm column: :status do
    state :unknown_scope
    state :new
  end
end

class Child
  include Mongoid::Document
  include AASM
  field :parent_id

  field :status, :type => String
  belongs_to :parent

  aasm column: :status do
    state :unknown_scope
    state :new
  end
end