How can I create references to objects in Ruby in ActiveRecords?

Question

I am a Java developer I've been learning Rails for the past few days. I have a Java EE application (Uses Hibernate for ORM) that I am trying to port to Rails. I have used scaffolding to generate a few of my models. But I have other models which contain references to other models. How do I define the relations? Can I scaffold that as well?

Here is an example for what I am trying to do.

public class Engine {
    private int valves;
    private int capacity;
    private int rpm;
}

I can scaffold the Engine class in ruby just by doing the following:

rails generate scaffold Engine valves:integer capacity:integer rpm:integer

Here is the tricky part for me:

public class Car {
    private Engine engine;
}

How do I scaffold the Car class in Ruby?

Answer 1

If I understand correctly you are looking for associations. Here's a great guide that you should read. The thing to understand here is that you define in your models how the they relate to each other with a series of methods described in that guide.

Here is what I would suggest you do:

rails generate scaffold Car <db columns>
rails generate model Engine valves:integer capacity:integer rpm:integer car_id:integer

In your two models:

class Car < ActiveRecord::Base
  has_one :engine
end 

class Engine < ActiveRecord::Base
  belongs_to :car
end

You can actually generate scaffold for both models...that will create controller and views. But in this case it might make sense to add

accepts_nested_attribues_for :engine

to your Car model instead. This will allow you to manage the manipulation of the Engine model from the controller and views of the Car model.

At any rate, I hope this helps you start to find what you need.