gistfile1.rb

class Entity < ActiveRecord::Base
  belongs_to :client
  has_many :group_members, :class_name => "Member", :foreign_key => "group_id"
  has_many :users, :through => :group_members, :source => :entity 

  alias_method :orig_users, :users

  def users
    entity.everyone_group? ? orig_users : client.users
  end
end