Hello Monks,

I have been wresting with a problem. I often need to parse and validate (string) data before inserting it into a DB. I've come to rely on Type::Tiny for this kind of validation.

In this case the data cannot be longer than x varchar(x). I often find the data is a empty etring, e.g. ''. If the data is an empty string, I would to rather return undef (null) than ''. In terms of terminology, I am not sure if this is a coercion or not. HTML::FormHandler has the notion of Transform(ations) but I haven't seen a means of appying transformations in the Moo world.

I have become stuck trying to finding a way to allow for a stirng to be either undefined, or if defined less than x or if an emtpy string, undefined.

It could be written a like (untested) this: $data = $_ eq '' ? undef : $_ < $x ? $_ : undef But I'd like to stick to the Types eco system albeit my grasp of it is somethimes failing. Here is my latest effort. The test warning because $_ is not numeric is tricky to side-step. 
use v5.22;
use warnings;

use Test::More;
use Test::Deep;
use Test::Warnings;
use lib qw(lib t);

use Type::Tiny;
use Types::Standard qw( Maybe Str );
use Types::Common::String qw( NonEmptyStr );
use Type::Params qw( compile_named );

=head2

The goal is to allow a "caption", if defined, should be less than $cap
+size.
If caption == '', I'd like to return the value as undef.

=cut

my $capsize = 2781;
# This will warn when $_ in not numeric
my $LongCaption = Type::Tiny->new(
    name       => 'Caption',
    constraint => sub {  length($_) < $capsize },
    message    => sub { "Caption needs to be less than $capsize charac
+ters" }
);
my $EmptyStr = "Type::Tiny"->new(
    name       => 'EmptyString',
    constraint => sub { $_ eq '' },
    message    => sub { "An empty string" }
);

$LongCaption->plus_coercions(
    $EmptyStr =>  sub {
        warn "Coercing";
        return undef;
        },
);

state $check = Type::Params::compile_named(
        caption => Maybe[$LongCaption],
);

my $text = '';
my $val = $LongCaption->assert_return( $text );
note $val;
is($val, undef, 'coerced into undef');

my $data = $check->( { caption => $text } );
cmp_deeply($data, { caption => undef }, 'coerced into undef');

done_testing;

[download]

Thanks in advance. I do hope I have not made a silly error.


Dermot

In reply to Coerce or transform with Types::Param by tomred

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