3023_spec.rb

require "spec_helper"

class User
  include Mongoid::Document

  has_and_belongs_to_many :cars, inverse_of: :users

  has_one :favorite_car, class_name: 'Car', inverse_of: :person
  
  before_validation :set_default_favorite_car, on: :create
  before_save :update_cars

  def set_default_favorite_car
    unless self.favorite_car
      self.favorite_car = Car.create!
    end
  end

  def updated_cars
    [favorite_car].compact
  end

  def update_cars
    _updated_cars = updated_cars
    self.cars = _updated_cars unless self.cars.map(&:id).sort == _updated_cars.map(&:id).sort
    true
  end

end

class Car
  include Mongoid::Document

  has_and_belongs_to_many :users, inverse_of: :cars
  belongs_to :person, class_name: 'User', inverse_of: :favorite_car#, autosave: true
end

describe User do

  before do
    @user = User.create!
  end

  describe "updating favorite_car" do

    before do
      @car = Car.create!
      @user.favorite_car = @car
      @user.save!
    end

    it "should update cars" do
      @user.cars.should eq([@car])
    end

    it "should update car_ids" do
      @user.car_ids.should eq([@car.id])
    end

    it "should persist new cars" do
      @user.reload.cars.should eq([@car])
    end

  end
end

describe Car do

  before do
    @car = Car.create!
  end

  describe "updating person" do

    before do
      @user = User.create!(favorite_car: @car)
      @car.person = @user
      @car.save!
    end

    it "should update users" do
      @car.users.should eq([@user])
    end

    it "should update user_ids" do
      @car.user_ids.should eq([@user.id])
    end

    it "should persist new users" do
      @car.reload.users.should eq([@user])
    end

  end
end