contactmodels.rb

class User < ActiveRecord::Base
  has_many :contacts
end

class Contact < ActiveRecord::Base
end

class DomesticContact < Contact
  validate :us_zip_format_validation
  
  private
  
  def us_zip_format_validation
    # errors.add(:zip, 'blah format valid stuff') if (validation_condition)
  end
end

class InternationalContact < Contact
  validate :intl_zip_format_validation
  
  private
  
  def intl_zip_format_validation
    # errors.add(:zip, 'blah format valid stuff') if (validation_condition)
  end
end