class Account < ActiveRecord::Base
  composed_of :plan,
              :allow_nil => false,
              :mapping => [
                #  Account                Plan
                %w(plan_name              name),
                %w(max_users              max_users),
                %w(max_repos              max_repos),
                %w(free_champagne         free_champagne),
               ],
              :constructor => Proc.new {|plan_name, max_users, max_repos, free_champagne |
                relation = Plan.where(:name => plan_name,
                                      :max_users => max_users,
                                      :max_repos => max_repos,
                                      :free_champagne => free_champagne)
                relation.present? ? relation.first : relation.build
              },
              :converter => Proc.new {|value|
                Plan.where(:name => value.is_a?(Array) ? value.first : value).first
              }

end

# This allows me do stuff like:
a = Account.new
a.plan = Plan.first
a.save

# and have all the plan's attributes reflected over as specified,
# but there be no explicit link in between the account instance and plan instance
# that last bit is useful if you want to offer completely custom plans for a minority of users