## Car
has_and_belongs_to_many :followers, :class_name => "User", :join_table => :car_followers

##User
has_and_belongs_to_many :followed_cars, :class_name => "Car", :join_table => :car_followers

## Table
create_table :car_followers, :id => false do |t|
      t.integer :car_id
      t.integer :user_id
    end

##
rpm = User.find 1
car = Car.find 4

>> rpm.followed_cars << car
>> rpm.followed_cars
[car]
>> car.followers
[] #dafux ?