Playing with a way of setting UI-specific default values in forms.

accounts_controller.rb

class AccountsController < ApplicationController
  include Authenticated

  before_action :populate_default_attributes, only: %i(new)

  expose :customer
  expose :accounts, ancestor: :customer
  expose :account

  # def new omitted, thanks to DecentExposure...

  private

  def populate_default_attributes
    account.attributes = {
      country_code: customer.default_country_code
    }
  end
end