Rails 4 to_xml issue with accessor overwriting in model

I have a problem with overwriting accessors in a model and using the to_xml method later on the model. The problem is, that to_xml seems to use the default getter method, rather than using read_attribute.

My model:

class Announcement < ActiveRecord::Base
  ...

  def created_at
    date = self[:created_at]
    "#{german_date(date)} #{german_time(date)} #{I18n.t(:clock)}"
  end

  ...
end

I'm using this, in order to easily run through parameters in my haml views, by always having the correct method for labels and text_fields. Because I need some attributes to be shown modified, I've overwritten the accessor.

-# Minified example ...
= form_for ...
  - %i(a b c d e).each do |attr|
    = f.label attr
    = f.text_field attr

The problem is: When I run to_xml, I get this problem:

NoMethodError: undefined method `xmlschema' for "15.03.2009 18:17 Uhr":String

Obviously, to_xml is using my custom getter rather than read_attribute(:created_at), which would give the correct value. I'm astonished to not have found this problem somewhere else, but IS there a solution to this problem?

There is a way using the options and a block with to_xml

announcment.to_xml(except: :created_at, procs: -> (options, record) {
  options[:builder].tag!("created-at", record.read_attribute(:created_at))
})

That's not pretty though. I would just use a decorator for your views and leave the model attribute methods alone, Draper works great with Rails 4.