Inheritance vs Polymorphism: Design Question for "IS A"


#1

Hi!

I have the next abstract composition:

Organization
ConsultingFirm IS A Organization
Client IS A Organization

User
ConsultingFirmUser IS A User
ClientUser IS A User

ConsultingFirmUser BELONGS TO ConsultingFirm
ClientUser BELONGS TO Client

ConsultingFirm HAS MANY ConsultingFirmUsers
Client HAS MANY ClientUsers

I don’t know how is the best way of implementing the “IS A” relationship
in Rails. What would you use? Inheritance or Polymorphism?

Thanks!


#2

On Wed, Apr 1, 2009 at 2:33 AM, Juan K.
removed_email_address@domain.invalid wrote:

ConsultingFirm HAS MANY ConsultingFirmUsers
Client HAS MANY ClientUsers

I don’t know how is the best way of implementing the “IS A” relationship
in Rails. What would you use? Inheritance or Polymorphism?

I would use a roles table and join model between users and roles.


Greg D.
http://destiney.com/


#3

Juan K. wrote:

I don’t know how is the best way of implementing the “IS A” relationship
in Rails. What would you use? Inheritance or Polymorphism?

There are two primary solutions provided by rails for this:

1: Single Table Inheritance (STI)
2: Polymorphic relationships.

The primary determining factor is how similar are the “subclasses” to
the abstract class. By this I mean do the subclasses add just a few
additional attributes to the superclass or do they add a lot. In the
former case STI may fit the bill very well and in the latter you’re
probably better off using a polymorphic relationship.

Google the two key words (STI and “Polymorphic Relationship”) and you
should find lots of information to help you decide what’s best in your
case. That is if either one fits, which I think one of them will.