Coercing ArrayRef[MyClass] from ArrayRef[HashRef] - perl

Question

In trying to answer How to instantiate Moose classes from a big hash, I think I have hit another place where I don't fully understand Moose type coercions. For some reason, the below code issues warnings:
You cannot coerce an attribute (departments) unless its type (ArrayRef[Company::Department]) has a coercion at ./test.pl line 12.
You cannot coerce an attribute (employees) unless its type (ArrayRef[Company::Person]) has a coercion at ./test.pl line 23.
but then succeeds.
#!/usr/bin/env perl
use warnings;
use strict;
package Company;
use Moose;
use Moose::Util::TypeConstraints;
has 'id' => (is => 'ro', isa => 'Num');
has 'name' => (is => 'ro', isa => 'Str');
has 'departments' => (is => 'ro', isa => 'ArrayRef[Company::Department]', coerce => 1);
coerce 'ArrayRef[Company::Department]',
from 'ArrayRef[HashRef]',
via { [ map { Company::Department->new($_) } #$_ ] };
package Company::Department;
use Moose;
has 'id' => (is => 'ro', isa => 'Num');
has 'name' => (is => 'ro', isa => 'Str');
has 'employees' => (is => 'ro', isa => 'ArrayRef[Company::Person]', coerce => 1);
package Company::Person;
use Moose;
use Moose::Util::TypeConstraints;
has 'id' => (is => 'ro', isa => 'Num');
has 'name' => (is => 'ro', isa => 'Str');
has 'age' => (is => 'ro', isa => 'Num');
coerce 'ArrayRef[Company::Person]',
from 'ArrayRef[HashRef]',
via { [ map { Company::Person->new($_) } #$_ ] };
package main;
my %hash = (
company => {
id => 1,
name => 'CorpInc',
departments => [
{
id => 1,
name => 'Sales',
employees => [
{
id => 1,
name => 'John Smith',
age => '30',
},
],
},
{
id => 2,
name => 'IT',
employees => [
{
id => 2,
name => 'Lucy Jones',
age => '28',
},
{
id => 3,
name => 'Miguel Cerveza',
age => '25',
},
],
},
],
}
);
my $company = Company->new($hash{company});
use Data::Dumper;
print Dumper $company;
How should this have been done? P.S. I tried simply doing
coerce 'Company::Department',
from 'HashRef',
via { Company::Department->new($_) };
but it died horribly.

Answer 1

Well, it doesn't succeed completely, and you should feel it when you'll try to update these fields with coerce => 1. That's why:
You cannot pass coerce => 1 unless the attribute's type constraint has
a coercion
Previously, this was accepted, and it sort of worked,
except that if you attempted to set the attribute after the object was
created, you would get a runtime error.
Now you will get an error when you attempt to define the attribute.
Still, I think I find the way to fix it, by introducing subtypes, first, and changing the order of packages, second:
package Company::Person;
use Moose;
use Moose::Util::TypeConstraints;
subtype 'ArrayRefCompanyPersons',
as 'ArrayRef[Company::Person]';
coerce 'ArrayRefCompanyPersons',
from 'ArrayRef[HashRef]',
via { [ map { Company::Person->new($_) } #$_ ] };
has 'id' => (is => 'ro', isa => 'Num');
has 'name' => (is => 'ro', isa => 'Str');
has 'age' => (is => 'ro', isa => 'Num');
package Company::Department;
use Moose;
has 'id' => (is => 'ro', isa => 'Num');
has 'name' => (is => 'ro', isa => 'Str');
has 'employees' => (is => 'ro', isa => 'ArrayRefCompanyPersons', coerce => 1);
package Company;
use Moose;
use Moose::Util::TypeConstraints;
subtype 'ArrayRefCompanyDepartments',
as 'ArrayRef[Company::Department]';
coerce 'ArrayRefCompanyDepartments',
from 'ArrayRef[HashRef]',
via { [ map { Company::Department->new($_) } #$_ ] };
has 'id' => (is => 'ro', isa => 'Num');
has 'name' => (is => 'ro', isa => 'Str');
has 'departments' => (is => 'ro', isa => 'ArrayRefCompanyDepartments', coerce => 1);
The rest of the code is the same as in your version. This works without any warnings, and more-o-less behaves like (again, I think) it should be.

Answer 2

From Moose::Manual::Type docs:
LOAD ORDER ISSUES
Because Moose types are defined at runtime, you may run into load order problems. In particular, you may want to use a class's type constraint before that type has been defined.
In order to ameliorate this problem, we recommend defining all of your custom types in one module, MyApp::Types, and then loading this module in all of your other modules.
So to add to raina77ow subtype & package order answer (+1) I would recommend creating a Company::Types module:
package Company::Types;
use Moose;
use Moose::Util::TypeConstraints;
subtype 'CompanyDepartments'
=> as 'ArrayRef[Company::Department]';
subtype 'CompanyPersons'
=> as 'ArrayRef[Company::Person]';
coerce 'CompanyDepartments'
=> from 'ArrayRef[HashRef]'
=> via {
require Company::Department;
[ map { Company::Department->new($_) } #$_ ];
};
coerce 'CompanyPersons'
=> from 'ArrayRef[HashRef]'
=> via { require Company::Person; [ map { Company::Person->new($_) } #$_ ] };
1;
And then put use Company::Types in all your Company:: classes.