Type Safety

We can use collection decoration to ensure that the items in a collection are of a certain type.

note

We find this usage superfluous most of the time considering static analysis tools can do a pretty good job these days. But it is also one of the most common objectives of people asking to have a custom Doctrine collection.

The Decorator Class

use Doctrine\Common\Collections\Collection;
use Rekalogika\Collections\Decorator\Decorator\CollectionDecorator;

/**
 * @extends CollectionDecorator<array-key,Book>
 */
class Books extends CollectionDecorator
{
    private static function assert(mixed $book): Book
    {
        if (!$book instanceof Book) {
            throw new \InvalidArgumentException('Invalid input');
        }

        return $book;
    }

    #[\Override]
    public function add(mixed $element): void
    {
        $this->getWrapped()->add(self::assert($element));
    }

    #[\Override]
    public function set(string|int $key, mixed $value): void
    {
        $this->getWrapped()->set($key, self::assert($value));
    }
}

Usage in the one-to-many Side

use Doctrine\Common\Collections\ArrayCollection;
use Doctrine\Common\Collections\Collection;
use Doctrine\ORM\Mapping as ORM;

#[ORM\Entity()]
class BookShelf
{
    /**
     * @var Collection<array-key,Book>
     */
    #[ORM\OneToMany(targetEntity: Book::class)]
    private Collection $books;

    public function __construct()
    {
        $this->books = new ArrayCollection();
    }

    public function getBooks(): Books
    {
        return new Books($this->books);
    }
}