Ruby on rails 试图通过接受\u嵌套的\u属性\u查找\u或\u创建？

我正在尝试

查找或创建一个关联的模型，该模型通过
接受
的嵌套属性被接受

我有一个旅行模型

class Trip < ActiveRecord::Base
  attr_accessible :organiser_attributes

  accepts_nested_attributes_for :organiser
  belongs_to :organiser, class_name: 'GuestUser', :autosave => true
end

现在我对
GuestUser
的电子邮件有一个唯一性约束（在验证和数据库级别）。因此，如果一个GuestUser创建了两个trip，我希望第二个trip应用于同一个GuestUser记录

我发现这似乎描述了实现这一目标的方法。然而，我似乎无法让它工作

在我的
Trip
车型中，我添加了：

class Trip < ActiveRecord::Base
  #other stuff ...

  belongs_to :organiser, class_name: 'GuestUser', autosave: true

  def autosave_associated_records_for_organiser
    # Find or create the organiser by name
    if new_organiser = GuestUser.find_by_email(organiser.email) then
      self.organiser = new_organiser
    else
      self.organiser.save!
    end
  end
end

失败，并显示以下消息：

Failures:
  1) TripsController POST create success if the guset user already exists should still create a trip
      Failure/Error: expect do
        count should have been changed by 1, but was changed by 0
      # ./spec/controllers/trips_controller_spec.rb:26:in `block (4 levels) in <top (required)>'

怎么回事？顺便说一句，我使用的是Rails 3.1.3。
通常情况下，您将
接受
的\u嵌套的\u属性\u放在作为关系父级的模型中（也称为关联的拥有类），即包含has\u many:children语句的模型中。
但我没有停止它的工作吗？我的意思是，它可以并且确实从父关联和子关联中起作用。关键是“嵌套”一词：您通常会在父关联中发现嵌套的子关联。。。嵌套，而不是相反
describe TripsController do
  describe "POST create success" do
    before :each do
      @guest_user = Factory.attributes_for(:guest_user)
      @trip = Factory.attributes_for(:trip)
      @valid_attr = @trip.merge(organiser_attributes: @guest_user)
    end

    describe "if the guest user already exists" do
      it "should still create a trip" do
        GuestUser.create! @guest_user
        expect do
          post :create, trip: @valid_attr, format: :json
        end.to change(Trip, :count).by(1)
      end
    end
  end
end

Failures:
  1) TripsController POST create success if the guset user already exists should still create a trip
      Failure/Error: expect do
        count should have been changed by 1, but was changed by 0
      # ./spec/controllers/trips_controller_spec.rb:26:in `block (4 levels) in <top (required)>'

  Processing by TripsController#create as JSON
  Parameters: {"trip"=>{"price"=>"3456", "origin_departure_time"=>"2011-12-13 18:08:15 +0000", "destination_arrival_time"=>"2011-12-13 20:08:15 +0000", "destination_departure_time"=>"2011-12-13 23:08:15 +0000", "origin_arrival_time"=>"2011-12-13 22:08:15 +0000", "organiser_attributes"=>{"email"=>"email@example.com", "name"=>"Peter Pan", "phone"=>"1234543534"}}}
   (0.0ms)  SAVEPOINT active_record_1
   (0.1ms)  SELECT 1 FROM "guest_users" WHERE "guest_users"."email" = 'email@example.com' LIMIT 1
   (0.0ms)  ROLLBACK TO SAVEPOINT active_record_1
Completed 422 Unprocessable Entity in 6ms (Views: 0.3ms | ActiveRecord: 0.1ms)
   (0.0ms)  SELECT COUNT(*) FROM "trips"