Rails - newbie association question with both has_many and HABTM models

Question

I have three models:

class Tenant < ActiveRecord::Base
  has_many :sites
end

class Site < ActiveRecord::Base
  belongs_to :tenant
  has_and_belongs_to_many :users
end

class User < ActiveRecord::Base
  has_and_belongs_to_many :sites
end

For Site and Users, I have a join table (sites_users).

Every Site has n Users. Every Tenant has n Sites.

To get a list of users for a specific site, it's easy:

t = Tenant.first
s = t.sites.first
s.users

But is there an association I can add to Tenant to provide a list of all users between all sites under that tenant? So that I can do:

t = Tenant.first
t.users

Answer 1

A number of people have asked for this, you'll see some discussion in the Rails Lighthouse Ticket #8994 of some developers trying to merge in the functionality of the nested_has_many_through plugin. If you're on Rails 2.3, the nested_has_many_through plugin might work for you, otherwise in Rails 3 you could write an ARel query to find the right set of studies.