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Design Patterns

The Factory Pattern: Centralising Object Creation

Delegate the responsibility of creating complex objects to a dedicated factory, keeping construction logic out of the domain and callers.

AAdam Ministrator
February 25, 2026
#factory-pattern#design-patterns

When constructing an object requires complex logic — choosing a concrete subclass, validating invariants, or coordinating multiple collaborators — that logic should not live in the caller or in the object itself. A Factory centralises creation, enforces invariants at construction time, and returns a fully initialised object. In DDD, factories are especially useful for creating aggregates whose initial state is non-trivial.

php
final class Order
{
    private function __construct(
        private readonly OrderId $id,
        private readonly CustomerId $customerId,
        private array $items = [],
    ) {}

    public static function place(CustomerId $customerId, array $items): self
    {
        if (empty($items)) {
            throw new \DomainException('An order must have at least one item.');
        }
        return new self(OrderId::generate(), $customerId, $items);
    }
}
Static factory method on an aggregate

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