Validating structured data

In an earlier post I discussed how HTML form processing, when sufficiently generalized, leads to processing structured data (by which I mean data in Perl-ish hashes and lists). Here is an example of some structured data:

my $user_record = {
   username => 'Joe Blow',
   occupation => 'Programmer',
   tags => ['Perl', 'programming', 'Moose' ],
   employer => {
      name => 'TechTronix',
      country => 'Utopia',
   },
   options => {
      flags => {
         opt_in => 1,
         email => 0,
      },
      cc_cards => [
         {
            type => 'Visa',
            number => '4248999900001010',
         },
         {
            type => 'MasterCard',
            number => '4335992034971010',
         },
      ],
   },
   addresses => [
      {
         street => 'First Street',
         city => 'Prime City',
         country => 'Utopia',
         id => 0,
      },
      {
         street => 'Second Street',
         city => 'Secondary City',
         country => 'Graustark',
         id => 1,
      },
      {
         street => 'Third Street',
         city => 'Tertiary City',
         country => 'Atlantis',
         id => 2,
      }
   ]
};

Here is the HTML::FormHandler form that defines field validators to process that structure:

{
   package Structured::Form;
   use HTML::FormHandler::Moose;
   extends 'HTML::FormHandler';

   has_field 'username';
   has_field 'occupation';
   has_field 'tags' => ( type => 'Repeatable' );
   has_field 'tags.contains' => ( type => 'Text' );
   has_field 'employer' => ( type => 'Compound' );
   has_field 'employer.name';
   has_field 'employer.country';
   has_field 'options' => ( type => 'Compound' );
   has_field 'options.flags' => ( type => 'Compound' );
   has_field 'options.flags.opt_in' => ( type => 'Boolean' );
   has_field 'options.flags.email' => ( type => 'Boolean' );
   has_field 'options.cc_cards' => ( type => 'Repeatable' );
   has_field 'options.cc_cards.type';
   has_field 'options.cc_cards.number';
   has_field 'addresses' => ( type => 'Repeatable' );
   has_field 'addresses.street';
   has_field 'addresses.city';
   has_field 'addresses.country';
   has_field 'addresses.id';

}

The names of the fields are flattened references to the elements of the structure, with special field types for Repeatable and Compound elements. These types of structures can be used to update a database with DBIx::Class (although there are limits, of course).

I've left off the actual validators, but they can be defined pretty easily using Moose types or other constraints.

  has_field 'cc_type' => ( apply => [ CCType ] );

It would probably be better to define some of the fields in a role or field, to keep some of the related validation in the same place. The validation of the credit card numbers depend on the type of the credit card, for example. Error messages can be retrieved from an array of error fields or plain error messages, but there need to be more flexible ways of getting those messages. I'm not exactly sure what people will want yet.

Real Soon Now (tm) I'm going to work on a KiokuDB model... So many programming tasks, so little time.