Input Verification with Data::Manager

A general commentary on the philosophy of data typing.

I don't believe anybody should be coding without use Moose these days. Moose grants so much power with type checking, coercion and attribute handling that it's pure folly to not use it. This, I presume, is not a new position.

Where Data::Verifier enters the fray is the adherence to Moose types. Types that can easily be defined and extended, as well as use the built-in types. You can also use coercions. This allows, at the verification step, a user input that resembles "tomorrow at 2pm" into a DateTime object (given sufficiently advanced DateTime coercion). It can even become more advanced, by having types such as "DateTimeAfterToday" where it checks, post-coercion, that it is indeed after the current date.

This is a type of verification and translation of user input that I don't believe was made possible (in Perl) before Moose. The guts of Data::Verifier reveal just how simple the code can be to accomplish significant work. There is the genius of this whole bag of tricks. It's very simple in its utilization, and gives much power.

A brief mention of Data::Manager.

Data::Manager is a glue module that marries Data::Verifier and Message::Stack. This handles the automatic parsing of Data::Verifier::Results and returns a populated Message::Stack with the configured and correct scopes.

Because of this thin layer of functionality, there isn't much to say about Data::Manager.

However, there is a lot to say in how to populate Data::Manager, and here is my preferred method!

Being lazy with Catalyst modeling.

In my applications, I have a Model::DataManager class which just builds out a Data::Manager object and returns it (per context, using Catalyst::Component::InstancePerContext). It looks at every model in my application for a verify attribute and then uses that. This means that I can, at any point, directly call verify on the model, or I can use Data::Manager.

And here is the very simple instance_per_context call in my DataManager model:

 with 'Catalyst::Component::InstancePerContext';

 sub build_per_context_instance {
     my ( $self, $c ) = @_; 
     # Time to get building! Look through every model and see if it has a
     # verifier attribute (to be extra safe, inspect the verifier to make
     # sure that it isa Data::Verifier)

     my %scopes = ();
     foreach my $name ( $c->models ) {
         next if $name eq 'DataManager';
         my $model = $c->model($name);
         next unless $model->can('meta');

         # This is intentionally naive for the sake of simple examples
         next unless $model->meta->has_attribute('verifier');

         $scopes{$name} = $model->verifier;
     my $dm = Data::Manager->new( verifiers => \%scopes );

     $self->data_manager( $dm );

     return $dm;

What this gives is a fully populated Data::Manager available at $c->model('DataManager') for usage. This just uses the model name as the scope identifier. In practice, I've found it to be more beneficial to have an attribute verification_scope that sets the scope. This can be overridden with Catalyst's configuration system, making it more general purpose and abstract.

When combined with nested parameters (See Catalyst::Plugin::Params::Nested the user input (through forms) is formatted like name="ModelName.field" and then verification happens easily:

 my $input = $c->req->params;
 # Though do verify this is what you expect
 foreach my $key ( keys %$input ) {
     if ( ref $input->{$key} eq 'HASH' ) {
         $c->model('DataManager')->verify( $key, $input->{$key} );

I actually have the above in a method in a separate package that extends Data::Manager, with some more specific checks that verify that the scope exists to verify, and some other enhancements that would really just complicate the example. I encourage the reader to build out a model that has all the application specific additions to make using Data::Manager simpler and more natural to use.

The results are in!

After you verify through Data::Manager, you have everything readily available.

$c->model("DataManager")->success being the most obvious of the useful values (which looks at every scope to guarantee success).

From there, you can serialize the results (a hash ref of Data::Verifier objects) and use them on failure (both in flash or stash, so you can honor Redirect-After-Post best practices).

The other non-obvious benefit is that often times you may find yourself working with a form or user-input that covers more than just a single model. This technique allows forms to automatically manage the verification of multiple models and return the results in a sane and packaged format.


Jay Shirley <> from Cold Hard Code