From: John Goetz <goetz.john@...>
Date: 2008-11-11T00:08:26+09:00
Subject: Re: design advice for newbie

Brian Candler wrote:
> This sounds fine to me, but for an alternative approach you could 
> consider Single Table Inheritance. That is, you have separate classes 
> for Student, Parent, Teacher etc, but they all live in the users table, 
> and can all be considered as a User. Teacher.find(...) will 
> automatically be restricted to User.find(:conditions => 
> "type='Teacher'")
> 
> http://ar.rubyonrails.com/classes/ActiveRecord/Base.html
> 
> Scroll down to "Single table inheritance" Also, the book "Agile Web 
> Development with Rails" has a section on this (but don't buy the 2nd 
> edition now, wait for the 3rd edition due in December)
> 
> However as already mentioned, this may be a Bad Idea. It's quite 
> possible for the same person to be both a student and a parent, or a 
> teacher and a trustee.
> 
> Person.has_and_belongs_to_many :roles may be a better way of modelling 
> this. Admittedly the SQL finders get a bit more awkward.

Thanks, Brian, for the direction. With Todd's advice also, I will 
investigate how to write up the has-and-belongs-to-many relationship and 
single table inheritance.
I already pre-purchased the 3rd edition of Agile Development with Rails 
and have a PDF of the beta release. It's helped me a lot, but I didn't 
get to that section yet. Time to hit the book again!

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