class Person
include Mongoid::document
field :name, type: String
has_many :addresses
end
class Address
include Mongoid::document
field :zip, type: String
belongs_to :Person
end
これだとダメ
user = User.new(:name => 'ABC')
user.addresses << Address.new(:zip => '100100')
user.save
adresssがinsertされない.
user = User.create!(:name => 'ABC')
user.addresses << Address.new(:zip => '100100')
user.save!
これで参照している子オブジェクトもinsertできた.