ここで遅延読み込みを使用できます。
class Book {
public $name;
private $_authors = null;
public function __constructor($name) {
$this->name = $name;
}
public function getAuthors() {
if ($this->_authors === null) {
$this->_authors = array();
/* database */
$this->_authors[] = new Author(/**/);
}
return $this->_authors;
}
// You can add some magic getter if you want to access authors as property
public function __get($key) {
if ($key === 'authors') {
return $this->getAuthors();
}
throw new Exception('Unknown property '.$key);
}
}
class Authors {
public $name;
private $_books = null;
public function __constructor($name) {
$this->name = $name;
}
public function getBooks() {
if ($this->_books === null) {
$this->_books = array();
/* database */
$this->_books[] = new Book(/**/);
}
return $this->_books;
}
// You can add some magic getter if you want to access books as property
public function __get($key) {
if ($key === 'books') {
return $this->getBooks();
}
throw new Exception('Unknown property '.$key);
}
}
これにより、著者/書籍が必要な場合にのみ読み込まれ、無限にループすることはありませんが、ここで別の問題に到達する可能性があります:
$author = new Author("Jon Doe");
$book = $author->books[0];
// assuming that book has one author
// $book->authors[0] will not be same object as $author
その解決策は、本と著者をロードするために何らかの第 3 のオブジェクトを使用することです。このオブジェクトは、既にロードされているオブジェクトを保存し、適切な場所に挿入します。
class Library {
private $_books = array();
private $_authors = array();
public function getBooksForAuthor($authorId) {
/* db query... */
$books = array();
while ($row = $stmt->fetch()) {
if (isset($this->_books[$row['id']]) {
$books[] = $this->_books[$row['id']];
} else {
$book = new Book($row);
$this->_books[$row['id']] = $book;
$books[] = $book;
}
}
return $books;
}
/* and similar authorsForBook() method */
}
class Author {
private $_data;
private $_library;
private $_books = null;
public function __constructor($data, $library) {
$this->_data = $data;
$this->_library = $library;
}
public function getBooks() {
if ($this->_books === null) {
$this->_books = $this->_library->getBooksForAuthor($this->_data['id']);
}
return $this->_books;
}
public function __get($key) {
if ($key === 'books') {
return $this->getBooks();
}
if (isset($this->_data[$key]) {
return $this->_data[$key];
}
throw new Exception('Unknown property '.$key);
}
}
/* and similar for book */