لبنات DDD الأساسية: الكيانات وكائنات القيمة

الجوهر التكتيكي

الهوية مقابل القيمة

كائن قيمة

<?php
final class Email {
    public function __construct(public readonly string $value) {
        if (!filter_var($value, FILTER_VALIDATE_EMAIL)) {
            throw new InvalidArgumentException("Invalid email: $value");
        }
    }
    public function equals(Email $other): bool {
        return strtolower($this->value) === strtolower($other->value);
    }
}
$a = new Email('Jane@Example.com');
var_dump($a->equals(new Email('jane@example.com'))); // true

المساواة بالقيمة

<?php
final class Money {
    public function __construct(
        public readonly int $cents,
        public readonly string $currency
    ) {}
    public function equals(Money $o): bool {
        return $this->cents === $o->cents && $this->currency === $o->currency;
    }
    public function add(Money $o): self {
        if ($this->currency !== $o->currency) {
            throw new DomainException('Currency mismatch');
        }
        return new self($this->cents + $o->cents, $this->currency);
    }
}
$sum = (new Money(500, 'USD'))->add(new Money(250, 'USD'));
echo $sum->cents, PHP_EOL; // 750

عدم القابلية للتغيير وطرائق «with»

<?php
final class DateRange {
    public function __construct(
        public readonly DateTimeImmutable $start,
        public readonly DateTimeImmutable $end
    ) {
        if ($end < $start) { throw new InvalidArgumentException('end before start'); }
    }
    public function withEnd(DateTimeImmutable $end): self {
        return new self($this->start, $end);
    }
}
$r = new DateRange(new DateTimeImmutable('2026-01-01'), new DateTimeImmutable('2026-01-10'));
$r2 = $r->withEnd(new DateTimeImmutable('2026-02-01'));
echo $r->end->format('Y-m-d'), ' / ', $r2->end->format('Y-m-d'), PHP_EOL;

كيان

<?php
final class Customer {
    private Email $email;
    public function __construct(
        public readonly string $id,
        Email $email
    ) { $this->email = $email; }

    public function changeEmail(Email $new): void { $this->email = $new; }
    public function email(): Email { return $this->email; }
    public function sameIdentityAs(Customer $o): bool { return $this->id === $o->id; }
}
$c = new Customer('cus_1', new Email('a@b.com'));
$c->changeEmail(new Email('c@d.com'));
echo $c->email()->value, PHP_EOL; // c@d.com

إنشاء الهوية

سلوك غني، لا بيانات فقيرة

<?php
final class Order {
    private string $status = 'open';
    public function __construct(public readonly string $id) {}
    public function cancel(): void {
        if ($this->status === 'shipped') {
            throw new DomainException('Cannot cancel a shipped order');
        }
        $this->status = 'cancelled';
    }
    public function status(): string { return $this->status; }
}
$o = new Order('o1');
$o->cancel();
echo $o->status(), PHP_EOL; // cancelled

كائنات القيمة في كل مكان

ملاحظة حول تخطيط التخزين

كائنات القيمة المركبة

<?php
final class Address {
    public function __construct(
        public readonly string $street,
        public readonly string $city,
        public readonly string $postcode
    ) {
        if ($postcode === '') { throw new InvalidArgumentException('postcode required'); }
    }
    public function equals(Address $o): bool {
        return $this->street === $o->street
            && $this->city === $o->city
            && $this->postcode === $o->postcode;
    }
    public function oneLine(): string {
        return "{$this->street}, {$this->city} {$this->postcode}";
    }
}
echo (new Address('1 Main St', 'Ankara', '06000'))->oneLine(), PHP_EOL;

اختبار سريع

مراجعة