I am using ruby on rails 3.1 and have 2 models, an event and a group. Each event has_many groups, but has to have at least one "master" group, where the column :is_master => true

Class Group < ActiveRecord::Base
  has_many :users
  belongs_to :event
  scope :master, where (:is_master => true)
end

Class Event< ActiveRecord::Base
  has_many :groups
  def master_group
     groups.master
  end
end

I want to be able to default all properties of the master group to the event, so for example, event.users.count should be the same as event.master_group.users.count.

Is there any way to do something like this? Can I do a has_many :through => master_group? Am I approaching this the wrong way?

Thanks!