境界づけられたコンテキストとコンテキストマッピング

戦略的DDD

ユビキタス言語

同じ言葉、異なるモデル

<?php
namespace Catalog;
final class Product {
    public function __construct(
        public readonly string $sku,
        public readonly string $description
    ) {}
}

namespace Inventory;
final class Product {
    public function __construct(
        public readonly string $sku,
        public readonly int $onHand
    ) {}
}

namespace App;
$c = new \Catalog\Product('A1', 'Blue mug');
$i = new \Inventory\Product('A1', 42);
echo $c->description, ' / ', $i->onHand, PHP_EOL;

大きな1つのモデルにしない理由

コンテキストマップ

コードにおけるコンフォーミスト

<?php
// Upstream's shape, used verbatim downstream (Conformist)
final class UpstreamUser {
    public function __construct(public readonly int $userId, public readonly string $login) {}
}
final class Greeter { // conforms: depends directly on upstream type
    public function greet(UpstreamUser $u): string {
        return "Hello {$u->login} (#{$u->userId})";
    }
}
echo (new Greeter())->greet(new UpstreamUser(7, 'jane')), PHP_EOL;

腐敗防止層

<?php
// Our clean domain model
final class Customer {
    public function __construct(public readonly string $id, public readonly string $name) {}
}
// Legacy/external shape we must not let leak in
$legacy = ['CUST_NO' => '0042', 'FULL_NM' => 'Jane Doe'];

final class LegacyCustomerAcl {
    public function toDomain(array $row): Customer {
        return new Customer($row['CUST_NO'], $row['FULL_NM']);
    }
}
$customer = (new LegacyCustomerAcl())->toDomain($legacy);
echo $customer->id, ' ', $customer->name, PHP_EOL;

コードにおける共有カーネル

<?php
namespace Shared; // small, jointly-owned kernel
final class Money {
    public function __construct(public readonly int $cents, public readonly string $cur) {}
    public function format(): string { return number_format($this->cents / 100, 2) . ' ' . $this->cur; }
}

namespace Billing;          // depends on the shared kernel
use Shared\Money;
function invoiceTotal(): Money { return new Money(4999, 'USD'); }

namespace Payroll;          // also depends on the SAME shared kernel
use Shared\Money;
function salary(): Money { return new Money(500000, 'USD'); }

PHPでコンテキストを統合する

<?php
// Published Language DTO from an upstream Open Host Service
final class PricingDto {
    public function __construct(public readonly string $sku, public readonly int $cents) {}
}
// Our downstream model
final class CatalogPrice {
    public function __construct(public readonly string $sku, public readonly float $amount) {}
}
final class PricingTranslator {
    public function translate(PricingDto $dto): CatalogPrice {
        return new CatalogPrice($dto->sku, $dto->cents / 100);
    }
}
$p = (new PricingTranslator())->translate(new PricingDto('A1', 1599));
echo $p->amount, PHP_EOL; // 15.99

コンテキストとアーキテクチャ

接点としてのイベント

<?php
// Published Language: a minimal stable contract
final class OrderPlacedEvent {
    public function __construct(public readonly string $orderId, public readonly int $cents) {}
}
// Downstream (Shipping context) maps it to its own model
final class Shipment {
    public function __construct(public readonly string $forOrder) {}
}
final class ShippingListener {
    public function on(OrderPlacedEvent $e): Shipment {
        return new Shipment($e->orderId); // ignores fields it doesn't need
    }
}
$shipment = (new ShippingListener())->on(new OrderPlacedEvent('o1', 1300));
echo 'shipment for ', $shipment->forOrder, PHP_EOL;

クイックチェック

まとめ