gistfile1.rb

class Signup
  has_one :account, :map => { :account_name => :name }
  has_one :user

  def on_save
    account.save
    user.save

    Membership.create :user_id => user.id, account.id
  end
end

signup = Signup.new :account_name => "omg"

if signup.save
  raise lol
end