The wraps_attribute Rails plugin lets you extract validation and normalisation of ActiveRecord attributes into a class.

The following is a simple class that validates and normalizes Australian phone numbers.

class PhoneNumber < String
  def initialize(value)
    super(value || '')
  end

  # Convert the phone number from local Australian format
  # (0x xxxx xxxx, or variations) to a compact international
  # format (61xxxxxxxxx).
  def normalize
    tr(' ()-', '').gsub(/\A\+/, '').gsub(/\A0/, '61')
  end

  # Returns true if the number is a valid Australian mobile phone number.
  # Australian mobiles take the form: 04xx xxx xxx
  def valid_australian_mobile?
    normalize =~ /\A614\d{8}\Z/ && true
  end

  # Returns true if the number is a valid Australian landline number.
  # Australian landline numbers take the form: (0n) xxxx xxxx
  # where n is the area code (2 for Sydney, 3 for Melbourne, etc.)
  def valid_australian_landline?
    normalize =~ /\A61[^4]\d{8}\Z/ && true
  end

  def valid?
    valid_australian_mobile? || valid_australian_landline?
  end

  # Return the phone number formatted for output.
  def format
    number = normalize
    if valid_australian_mobile?
      "0#{number[2..4]} #{number[5..7]} #{number[8..10]}"
    elsif valid_australian_landline?
      "(0#{number[2..2]}) #{number[3..6]} #{number[7..10]}"
    else
      self
    end
  end
end

In your ActiveRecord model, you just do something like this:

class Person < ActiveRecord::Base
  wraps_attribute :phone_number, PhoneNumber
end

That does a couple of things:

1. Before validations are done, the normalize method is used to convert the phone number to a canonical format to be stored in the database.

2. The valid method is used to validate the number when ActiveRecord does its validations.

If you want to use a different method than valid? for validation, use something like:

wraps_attribute :mobile_number, PhoneNumber, :validate => :valid_australian_mobile?

You can also turn off automatic validation entirely with:

wraps_attribute :phone_number, PhoneNumber, :validate => false

You can allow blank values for the attribute with:

wraps_attribute :phone_number, PhoneNumber, :allow_blank => true

You can specify a custom ActiveRecord error message to use on validation failure with:

wraps_attribute :phone_number, PhoneNumber, :message => "must be a valid Australian phone number"

Regular ActiveRecord validations also work with wrapped attributes. The attribute is normalized before validations are run.

ruby script/plugin install git://github.com/notahat/wraps_attribute.git