How to insert two associated instances in to corresponding tables by using a Migration?

I have two ActiveRecode model, Car and User, which has many-to-one association:

class Car < ActiveRecord::Base
  has_many :users
  ...
end

class User < ActiveRecord::Base
  belongs_to :car
  ...
end

And, I have two tables in database, cars and users. users table has attribute car_id

I would like to have a migration which will insert a car instance to the cars table, meanwhile, there will be a user instance created which has the association with the car instance and will then 开发者_运维知识库be inserted to the users table. How to do this in a migration?

That's by run this migration, both the car instance and its associated user instance will be stored in the corresponding tables in database.

I am using Rails 3.

example of migrations

class FillCarsAndUsers < ActiveRecord::Migration
  def self.up
    #if you have a Corresponding class for table 
    Corresponding.find(:all).each do |cor|
      #save data

      car = Car.create(...) #you may save old car id, if need "Car.create(:id => cor.car_id, ...)"
      User.create(:car_id => car.id, ...)
      ...
      User.create(:car_id => car.id, ...)
    end

  end

  def self.down
  end
end

Try like this

data = {'car1' => ['user1', 'user2'], 'car2' => ['user3'], 'car3' => ['user4']}
data.each do |car, users|
  car_obj = Car.create(:name => car)
  users.each do |user|
    User.create(:name => user, :car_id => car_obj.id)
  end
end