Simple has_many :through

gistfile1.rb

###########
# Classes #
###########

class Group < ActiveRecord::Base
  has_many :memberships,
           :class_name => 'GroupUser'
  has_many :users,
    :through => :memberships,
    :source => :user
  has_many :owners,
    :through => :memberships,
    :source => :user,
    :conditions => {'groups_users.role' => GroupUser::OWNER_ROLE}
  has_many :newbies,
    :through => :memberships,
    :source => :user,
    :conditions => {'groups_users.role' => GroupUser::NEWBIE_ROLE}
end

class User < ActiveRecord::Base
  has_many :group_memberships,
    :class_name => 'GroupUser',
    :dependent => :destroy
  has_many :groups,
    :through => :group_memberships
end

class GroupUser < ActiveRecord::Base
  OWNER_ROLE = 'owner'
  NEWBIE_ROLE = 'newbie'

  belongs_to :group
  belongs_to :user
end

########
# So, I want a "group" to always have an owner, here's how I'm doing it now,
# I'm not enamored of this approach
########

# Add an attr_accessor and a callback to the Group class

class Group < ActiveRecord::Base
  # Same shit as above

  # New stuff
  attr_accessor :created_by
  after_create :set_owner

  private
  def after_create
    memberships.create(:user => created_by) do |m|
      m.role = GroupUser::OWNER_ROLE
    end
  end
end

# For Newbies, the shit is a little trickier, because I want to do
# things like validate roles for adding newbies, send invitation
# emails, etc.  So, instead of trying to do all of that shit in 
# the join model, I created a new class

class GroupNewbie
  extend ActiveModel::Callbacks
  include ActiveModel::Validations

  # Attributes
  attr_accessor :group_id, :created_by, :email, :user, :group

  # Bunch of validations
  # Bunch of callbacks

  def save
    _run_create_callbacks do
      GroupUser.create(:user => user, :group => group) do |gu|
        gu.role = GroupUser::NEWBIE_ROLE
      end
    end if valid?
  end
end

# Then, in the controller, I can just do:
newb = GroupNewbie.new(:group_id => 1, :created_by => current_user, :email => '[email protected]')

if newb.save
  # blah
else
  # worse blah
end

# So, that's where I'm at now.  What I'd like to do... what feels most "Rails-ish"
# is this:

# Adding a newbie
# This does create the GroupUser record, but it doesn't populate the 'role' attribute
group = Group.find(params[:id])
group.newbies << User.find_by_email('[email protected]')

# Adding a new group
# This creates the Group record, but does NOT create the GroupUser record.  Leading to
# the code mentioned above
group = current_user.groups.build(params[:group])
group.save

# What do you think?