Rails - Jan 2008 - resources, has_many :through and extra attributes on 'join model'

Hi,

I found a small ''problem'' to which I think I found a solution.
But the solution feels a bit hacky.
I would like some feedback on it.

Say I have Groups & Users.
A group has many users, but a user can also belong to many groups.
Also, the role a user has in a group should be known.

   1. class Group < ActiveRecord::Base
   2.   has_many :memberships
   3.   has_many :users, :through => :memberships
   4. end
   5.
   6. class User < ActiveRecord::Base
   7.   has_many :memberships
   8.   has_many :groups, :through => :memberships
   9. end
  10.
  11. class Membership < ActiveRecord::Base
  12.   belongs_to :group
  13.   belongs_to :user
  14.   validates_uniqueness_of :user_id, :scope => :group_id
  15.
  16.   # this model has a field "role" which describes the role a
user has in the group
  17. end

Now, this suffices for the database and the model, but in my routes
file I don''t want to expose memberships as resources (since they are
kind of artificial), so:

   1.   map.resources :groups do |group|
   2.     group.resources :users
   3.   end
   4.
   5.   map.resources :users do |user|
   6.     user.resources :groups
   7.   end

This works, I can now see which users are in a group(on /groups/2/
users), but there is no way to see what role they have.

My solution would be to give users a virtual attribute (role) which
should get filled in when they are acquired by a group.

something along the lines of

   1. class Group < ActiveRecord::Base
   2.   has_many :memberships
   3.   has_many :users, :through => :memberships
   4.
   5.   def users_with_roles
   6.     array = []
   7.     memberships.each do |membership|
   8.       user = membership.user
   9.       user.role = membership.role
  10.       array << user
  11.     end
  12.     array
  13.   end
  14. end

Now, I can use @group.users_with_roles in my userscontroller''s index
action and display the list of users, including their role in this
group.

Of course this needs some changes for finding single users also, and
code to handle saving in case of adding users to a group.

But before I go that way I need to be assured this is the/a way to go.
Like I said, it feels very hacky, so I guess there should be a better
way to do this.

Any thoughts on this subject?
Like I said, I don''t want to expose memberships to the outside world,
just users & groups.

Thanks, Mathijs

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