perl-patterns

Background knowledge for Perl/Moose projects. Auto-loaded for pattern guidance.

Moose Class Template

package MyApp::Domain::Entity;
use Moose;
use namespace::autoclean;
has 'id'   => (is => 'ro', isa => 'Int', required => 1);
has 'name' => (is => 'rw', isa => 'Str', required => 1);
sub validate { my ($self) = @_; die "Empty name" unless length($self->name); 1 }
__PACKAGE__->meta->make_immutable;
1;

Error Handling -- Always Try::Tiny, never bare eval {}

use Try::Tiny;
try { $repo->save($entity) }
catch { $logger->error("Save failed: $_"); die "Could not save: $_" };

Array/Hash Reference Rules

| Pattern | Wrong | Correct | |---------|-------|---------| | Iterate | my @arr = @$ref; foreach (@arr) | foreach (@$ref) | | Chunk | my @copy = @$ref; splice(...) | @{$ref}[$i..$end] | | Return | return @array | return \@array | | Pass | func(@array) | func(\@array) |

DDD Layer Pattern

Domain (pure logic) -> Repository (data access) -> Mapper (transform) -> Controller (HTTP)

• Domain: Moose classes, no DB imports
• Repository: DBIx::Class queries, returns domain objects
• Mapper: Transforms between domain and presentation
• Controller: Route handlers, calls repository/mapper

DateTime Safety

# WITH InflateColumn::DateTime in schema
$rs->create({ date_field => DateTime->now });

# WITHOUT InflateColumn::DateTime
use MyApp::Util::DateTime qw(formatOracleDateTime);
$rs->create({ date_field => formatOracleDateTime(DateTime->now) });

Never use string-returning now() functions for database fields.

Common Anti-Patterns

• HashRefInflator bypasses domain logic -- use repositories
• Direct DB access from controllers -- use repository layer
• Exporter for OO modules -- use Moose
• eval {} without Try::Tiny -- loses error context
• Copying large arrays -- iterate references directly