using NanoStore::Model to do basic relations.

models.rb

class Car < NanoStore::Model
  attribute :name
  attribute :year
  attribute :user_id

  def user
    User.find(:id => user_id).first
  end

  def self.create(name, year, user_id)
    car = Car.new
    car.name = name
    car.year = year
    car.user_id = user_id
    car
  end
end

class User < NanoStore::Model
  attribute :id
  attribute :name
  attribute :age
  attribute :created_at
  attribute :cars_bag_name

  def self.create(id, name, age, cars_bag_name)
    user = User.new
    user.name = name
    user.age  = age
    user.id = id
    user.created_at = Time.now
    user.cars_bag_name = cars_bag_name
    user
  end

  def cars
    cars = []
    bag = NanoStore.shared_store.bagWithName(cars_bag_name)
    if bag
      bag.savedObjects.merge(bag.unsavedObjects).each do |k, v|
        cars << v
      end
    end
    cars
  end
end

REPL

(main)> bag = NanoStore::Bag.bag
=> #<NanoStore::Bag:0x8c930b0>
(main)> NanoStore.shared_store.addObject(bag, error:nil)
=> true
(main)> bag.setName "cars"
=> #<NanoStore::Bag:0x8c930b0>
(main)> user = User.create(8, 'demo', 23, bag.name)
=> #<User:0x8c93800>
(main)> user.save
=> #<User:0x8c93800>
(main)> car = Car.create('toyota', 1986, user.id)
=> #<Car:0x8db1c00>
(main)> bag << car
=> #<NanoStore::Bag:0x8c930b0>
(main)> car = Car.create('toyota 2', 1988, user.id)
=> #<Car:0x8db2030>
(main)> bag << car
=> #<NanoStore::Bag:0x8c930b0>
(main)> bag.save
=> true
(main)> user.cars
=> [#<Car:0x8c7d040>, #<Car:0x8c7a3f0>]