#[Entity, Table]
class SimpleBook
{
    #[Column, Id, GeneratedValue]
    private readonly int $id;

    #[Column]
    public readonly string $title;

    #[ManyToOne, JoinColumn(nullable: false)]
    private readonly Author $author;

    public function getId(): int
    {
        return $this->id;
    }

    public function getTitle(): string
    {
        return $this->title;
    }

    public function getAuthor(): Author
    {
        return $this->author;
    }
}

class SimpleBook extends \Entity\SimpleBook implements \Doctrine\ORM\Proxy\Proxy
{
    // ...

    public function __construct(?\Closure $initializer = null, ?\Closure $cloner = null)
    {
        unset($this->title);

        $this->__initializer__ = $initializer;
        $this->__cloner__      = $cloner;
    }
}