limiting who and see/update which record

Hello, all,

Say I own a freelance article editing company that help my clients
editing their articles to a certain standard. And my employees are
editors. a Article Model, an Assignment Model, and then an Editor
Model. Most of the time one article is edited by one Editor ( and this
arrangement is called an Assignment). Sometimes, things get rushy and
we put a few editors for one article.

so I guess I will have a many Editors to many Articles relationship by
using the Has_many :through => :assignments

class Editor < ActiveRecord::Base
  has_many :assignments
  has_many :articles, :through => :assignments
end

class Assignment < ActiveRecord::Base
  belongs_to :article
  belongs_to :editor
end

class Article < ActiveRecord::Base
  has_many :assignments
  has_many :editors, :through => :assignments
end

If I want only relevant editor(s) to see an article--relevant being
defined as the editor(s) is assigned to that very artcile--and also to
update that artcile, as needed for editing it, where would one put
such a mechanism (ApplicationController / Model / elsewhere)? And how
would such a mechanism work?

Thanks@

Thanks Marnen, I will check it out.