From: Lou Vanek <vanek@...>
Date: 2005-11-07T07:05:28+09:00
Subject: Re: Basic help with understanding RoR Inheritance

You might try one 'Vehicle' table that holds all common
fields, and a bunch of other tables (Cars, Trucks, Motorcycles, etc.)
common to each vehicle that only holds fields specific to that type of vehicle.


class Trucks < ActiveRecord::Base
    has_one :vehicle
    . . .
end

class Cars < ActiveRecord::Base
    has_one :vehicle
    . . .
end

class Motorcycles < ActiveRecord::Base
    has_one :vehicle
    . . .
end

class Vehicles < ActiveRecord::Base
    #belongs_to :truck # this probably wouldn't work. Not sure what to do here.
    #fields common to all: trucks, cars, motorcycles, etc.
    . . .
end

I haven't tried this type of schema but it seems like it might work.

-lv


TomRossi7 wrote:

> I'm sorry for the newbie question, but I can't seem to find a basic
> enough explanation for what I am looking for.  Basically, I am trying
> to understand Ruby on Rails Single Table Inheritance and the required
> database structure for easy ActiveRecord integration.  Here is a simple
> example that I would be very grateful for assistance:
> 
> Imagine you want to create an application built for tracking vehicle
> information.  You have a super-class Vehicle with attributes like VIN,
> manufacturer, manufacturer date etc. -- all of the attributes that are
> shared by all vehicles.  Then you have sub-classes like car, truck,
> motorcycle, etc.  These sub-classes have unique attributes like maybe a
> "towing capacity"  for trucks [Granted, the attributes aren't that
> dissimilar between a car and a truck, but this is just an example].
> 
> So, how would this best be modeled in the database and RoR?  I am
> thinking a model (class) for Vehicle, Car, Truck, Motorcyle.  The
> tables would be vehicles, cars, trucks, motorcylces.  They each would
> have id's and the vehicle table would track for each id the "type" of
> vehicle.
> 
> Am I on the right track?
> 
> Thanks,
> Tom
> 
> 
>