# Re: enforce mutual exclusivity **URL:** \ **Category:** Ruby\ **Created:** [September 8, 2007, 12:14am UTC](https://www.ruby-forum.com/t/re-enforce-mutual-exclusivity/114112 "2007-09-08T00:14:55Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![mwalsh](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/91b2a8/32.png) [@mwalsh](https://www.ruby-forum.com/u/mwalsh)\ **Post date:** [September 8, 2007, 12:14am UTC](https://www.ruby-forum.com/t/re-enforce-mutual-exclusivity/114112/1 "2007-09-08T00:14:55Z")
Toby, Seeing as ActiveRecord is part of Rails, you ought to post this question to the “Ruby on Rails: Talk” group. ----- Original Message ---- From: Toby O’Rourke [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) To: ruby-talk ML [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) Sent: Friday, September 7, 2007 3:59:53 PM Subject: enforce mutual exclusivity Hi, First post, sorry if this is the wrong place or has been answered before. I’m using ActiveRecord and I want to enforce mutual exclusivity on a has\_and\_belongs\_to\_many. A concrete example: I have a User which can have one or more Roles (student, tutor, headmaster, administrator etc). However if a user is a student they cannot hold any other role. I was hoping to find something like validate\_exclusive but that doesn’t appear to exist. Can anyone suggest how I can implement this. Otherwise, is there a better pattern I could use to model this? Many thanks, Toby.