Registration of user and account: Registration form object

registration.rb

# see https://gist.github.com/RichardJordan/9059633 for explanation
# -----------------------------------------------------------------

class Registration
  extend  ActiveModel::Naming
  include ActiveModel::Model
  include ActiveModel::Validations::Callbacks
  include ActiveModel::ForbiddenAttributesProtection

  attr_accessor :email, :password, :password_confirmation,
                :shortname, :fullname
  attr_reader   :saved
  attr_writer   :account_source, :user_source

  delegate :email=, :password=, :password_confirmation=,
           :email,  :password,  :password_confirmation, to: :user

  delegate :shortname=, :fullname=, 
           :shortname,  :fullname, to: :account

  before_validation :downcase_email_and_shortname
  
  validates :email, presence: true, email_format: true
  
  validates :password_confirmation, presence: true
  validates :password,
    presence: true,
    length: {
      minimum: 6,
      allow_blank: false,
      message: "must be at least 6 characters"
    }
  
  validates :fullname, length: { maximum: 250 }

  validates :shortname,
    presence: true,
    length: { minimum: 5, maximum: 50,
      message: "Short name must be 5-50 characters long" },
    format: /\A[A-Za-z0-9_-]+\Z/
  
  validate  :verify_unique_email
  validate  :verify_unique_shortname

  def account
    @account ||= account_source.call
  end

  def attributes
    { email: email, password: password,
      password_confirmation: password_confirmation,
      fullname: fullname, shortname: shortname }
  end

  def attributes=(attrs)
    sanitize_for_mass_assignment(attrs).each { |k,v| send("#{k}=", v) }
  end

  def new_record?
    !saved
  end

  def persisted?
    false
  end

  def save!
    @saved = account.save! && user.save!
  end

  def user
    @user ||= user_source.call
  end

  private

  def account_source
    @account_source ||= Account.public_method(:new)
  end

  def downcase_email_and_shortname
    email.downcase! if email
    shortname.downcase! if shortname
  end

  def user_source
    @user_source ||= User.public_method(:new)
  end

  def verify_unique_email
    if email && (User.exists? email: email)
      errors.add :email, "has already been signed up"
    end
  end

  def verify_unique_shortname
    if shortname && (Account.exists? shortname: shortname)
      errors.add :shortname, "has already been taken"
    end
  end
end