# Class can be many other..classes **URL:** \ **Category:** Rails\ **Created:** [May 12, 2007, 9:31pm UTC](https://www.ruby-forum.com/t/class-can-be-many-other-classes/104008 "2007-05-12T21:31:20Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![stepheneb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/71e660/32.png) [@stepheneb](https://www.ruby-forum.com/u/stepheneb)\ **Post date:** [May 12, 2007, 9:31pm UTC](https://www.ruby-forum.com/t/class-can-be-many-other-classes/104008/1 "2007-05-12T21:31:20Z")
Hey All, Before I go off on a tangent, I thought it best to see if anyone has a pattern for this already. An example should explain all: Let’s say I have a Person class and a person can be both a Teacher and a Performer. I feel that Teacher and Performer are classes in their own right as they have other things associated with them. Including all attributes and associations under the User class will get real messy, real quick. At first I experimented with STI but obviously a class can only be one type. I could also use standard associations and have this kind of set up: person = Person.find(1) person.teacher.level person.performer.styles This could prove to be the most straight-foward way of doing it, but I can’t help feeling that the definitions aren’t representative of the domain - and that kinda bothers me. I feel like saying “a Person can be a Teacher and/or a Performer”… Anyway, I’d be very interested in anyone’s thoughts on this. If there is a pattern out there for this that would apply to ActiveRecord then I’m poised to code it up. Cheers, Steve ---
**Author:** ![stepheneb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/71e660/32.png) [@stepheneb](https://www.ruby-forum.com/u/stepheneb)\ **Post date:** [May 12, 2007, 9:38pm UTC](https://www.ruby-forum.com/t/class-can-be-many-other-classes/104008/2 "2007-05-12T21:38:20Z")
I don’t think inheritance/polymorphism solve your problem. You might look to roles (has\_many :roles, :through =\> :join\_table). ---
**Author:** ![stepheneb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/71e660/32.png) [@stepheneb](https://www.ruby-forum.com/u/stepheneb)\ **Post date:** [May 12, 2007, 9:48pm UTC](https://www.ruby-forum.com/t/class-can-be-many-other-classes/104008/3 "2007-05-12T21:48:21Z")
> I don’t think inheritance/polymorphism solve your problem. > I agree. > look to roles (has\_many :roles, :through =\> :join\_table). > Hmm… roles do sound more promising… I think that inheritence could > be used then. If I say that Teachers and Performers are Roles that > People have, it feels a lot more natural. See? It’s always best to ask. You should have seen some of the ideas I was having for what’s actually a straight forward problem… Cheers, Steve ---
**Author:** ![stepheneb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/71e660/32.png) [@stepheneb](https://www.ruby-forum.com/u/stepheneb)\ **Post date:** [May 12, 2007, 9:49pm UTC](https://www.ruby-forum.com/t/class-can-be-many-other-classes/104008/4 "2007-05-12T21:49:21Z")
Steve > Let’s say I have a Person class and a person can be > both a Teacher and a Performer. I’m sure there are better ways but what about : (untested) ``` class Person < ActiveRecord::Base has_many :classes has_many :performances def teacher? ; classes .empty? end def performer? ; performances.empty? end end ``` ## Alain R. [http://blog.ravet.com](http://blog.ravet.com) ---
**Author:** ![stepheneb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/71e660/32.png) [@stepheneb](https://www.ruby-forum.com/u/stepheneb)\ **Post date:** [May 12, 2007, 10:07pm UTC](https://www.ruby-forum.com/t/class-can-be-many-other-classes/104008/5 "2007-05-12T22:07:22Z")
Steve, > Yeah that’s a nice idea but my main concern is that as the > application > grows, it will get messy with this kind of set up. For example, if > a > Person could be a Student I’d need to add yet more relationships and > attributes. Personally I prefer the compact style of my first post, but I guess you could “modularize”/“role-arize” it : (untested) ``` class Person < ActiveRecord::Base include Teacher, Performer, Student end module Teacher def self.included(base) base.has_many :classes, :dependent => :destroy end def teacher? ; !classes.empty? end end module Student .. module Performer .. ``` Even with 3 roles I still prefer the compactness of : ``` class Person < ActiveRecord::Base has_many :classes , :dependent => :destroy has_many :performances, :dependent => :destroy has_many :enrolments , :dependent => :destroy def teacher? ; !classes .empty? end def performer? ; !performances.empty? end def student? ; !enrolments .empty? end end ``` ## Alain R. [http://blog.ravet.com](http://blog.ravet.com) ---
**Author:** ![stepheneb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/71e660/32.png) [@stepheneb](https://www.ruby-forum.com/u/stepheneb)\ **Post date:** [May 12, 2007, 9:56pm UTC](https://www.ruby-forum.com/t/class-can-be-many-other-classes/104008/6 "2007-05-12T21:56:22Z")
Alain, Yeah that’s a nice idea but my main concern is that as the application grows, it will get messy with this kind of set up. For example, if a Person could be a Student I’d need to add yet more relationships and attributes. The Roles idea suggested by s.ross will allow me to organise my classes neatly and there’s room for expansion as the application grows. Cheers, Steve ---
**Author:** ![stepheneb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/71e660/32.png) [@stepheneb](https://www.ruby-forum.com/u/stepheneb)\ **Post date:** [May 12, 2007, 10:46pm UTC](https://www.ruby-forum.com/t/class-can-be-many-other-classes/104008/7 "2007-05-12T22:46:25Z")
Steve, > I originally thought that I wanted to be able to do this: > Teacher.find(:all) The simplest shortest (but slowest) way that works : teachers = Person.find(:all).select(&:teacher?) (Don’t use if you have more than xxx people in your DB) ## Alain R. [http://blog.ravet.com](http://blog.ravet.com) ---
**Author:** ![stepheneb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/71e660/32.png) [@stepheneb](https://www.ruby-forum.com/u/stepheneb)\ **Post date:** [May 12, 2007, 10:28pm UTC](https://www.ruby-forum.com/t/class-can-be-many-other-classes/104008/8 "2007-05-12T22:28:24Z")
Actually, you know what? I think you may be right. I just started explaining why I thought the multiple model idea was better and realised that it was actually no better than my original idea of using relationships. I want to avoid this: person.teacher.regular\_classes So your idea of putting all the relationships in the Person class achieves that. I originally thought that I wanted to be able to do this: Teacher.find(:all) but to be honest, I think I might be better off having ‘teacher’, ‘student’, ‘performer’ attributes in my people table and use those. Seeing as a Person could be all 3 roles there’s nothing messy about having the attributes and associations in the same class. Cheers, Steve ---
**Author:** ![stepheneb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/71e660/32.png) [@stepheneb](https://www.ruby-forum.com/u/stepheneb)\ **Post date:** [May 12, 2007, 11:10pm UTC](https://www.ruby-forum.com/t/class-can-be-many-other-classes/104008/9 "2007-05-12T23:10:27Z")
If you know that the only three roles a person can assume are teacher, student, and performer, then you’re in good shape with this solution. It’s when you get a few months down the road and you have to add hall\_monitor or class\_clown that you begin to have issues with hard-typing instead of relational (role-based).