class Person
  include Mongoid::Document
  field :name, type: String
  embeds_many :addresses
end

class Address
  include Mongoid::Document
  field :address, type: String
  embedded_in :person
  validates :person, presence: true
end

p = Person.create!(name: 'Person')
p.addresses.build(address: '1')
p.addresses.build(address: '2')
p.addresses = p.addresses
p.save!