gistfile1.rb

  validates_each :iban do | record, attr, value |
    record.errors.add attr, 'IBAN is mandatory' and next if value.blank?
    # IBAN code should start with country code (2letters)
    record.errors.add attr, 'Country code is missing from the IBAN code' and next unless value.to_s =~ /^[A-Z]{2}/i
    iban = value.gsub(/[A-Z]/) { |p| (p.respond_to?(:ord) ? p.ord : p[0]) - 55 }
    record.errors.add attr, 'Invalid IBAN format' unless (iban[6..iban.length-1].to_s+iban[0..5].to_s).to_i % 97 == 1
  end