public function getAttributes($book): array
    {
        return [
            "title" => function (array $book) {
                return $book["title"];
            },
            "isbn13" => function (array $book) {
                return $book["isbn13"];
            },
            "releaseDate" => function (array $book) {
                return $book["release_date"];
            },
            "hardCover" => function (array $book) {
                return $book["hard_cover"];
            },
            "pages" => function (array $book) {
                return (int) $book["pages"];
            },
        ];
    }