PHP5 Object-Oriented Programming

I have started building a few applications using OO programing in PHP, however I am not sure If I am doing it the standard way.

Heres an example, if I had a book class

    class book{

            private $name;
            private $id;
            private $isbn;
    }

There are two scenarios, one, I want to add a brand new book to my database...

should I a) use a function within my new class to create the new book... ie.

    $book = new book;

    $book->addAsNew($name, $isbn);

Or should I B) have a function completely independent of the class that adds a new book?

Secondly.. when opening my book class, should I have A) a constructor

    function __construct( $bookId ){

            //Call mysql DB and set $name and $isbn var based on $bookId

    }

    ...

    $book = new book( $bookId );

of should I b) have a separate function..

    class boo开发者_如何学运维k{

            private $name;
            private $id;
            private $isbn;

            public initiated = 0;

            function initiate( $bookId ){

                    //Load $name and $isbn from DB based on $bookId

                    $initiated = 1;
            }
    }

    ...

    $book = new book;

    $book = initiate( $bookId );

Is there a standard way most programmers would do this? or is it just mainly at the discretion of the programmer?

---

You can add parameters to the constructor too, so you could write

book = new Book($name, $isbn). 

But in this case, I'd choose to have a class with separate properties, like you have, and create a separate factory class or function to instantiate the book objects.

The same goes for B. Don't put the DB queries in this class. Create a separate BookData object that can act as a factory. It can query the database and return the book object(s). Of course, if you feel a factory class is over complicated, you can create a function too, but hey, you wanted to go OO. ;-)

---

What you are doing is creating models and data mappers, please refer to:

1. http://www.devshed.com/c/a/PHP/Implementing-the-Data-Mapper-Design-Pattern-in-PHP-5/
2. http://www.doctrine-project.org/ - http://www.doctrine-project.org/docs/orm/2.0/en/tutorials/getting-started-xml-edition.html

So your book class is a model, and that model needs to be stored somewhere. Pseudo-code would be:

$book = new Book();
$book
    ->setName($name)
    ->setId($id)
    ->setISBN($isbn);

$bookDataMapper = new BookDataMapper();
$bookDataMapper->save($book);

---

You could do both!

Calling initiate from the constructor

function __construct( $bookId = null) {
   if ($bookId) {
      $this->initiate($bookId);
   }
}

From a OOP perspective this is nice, because it prevents an empty object.

empty object: An object that issn't a real live object yet, but exists only in code.

But because the $bookId parameter is optional, an empty object is still possible, allowing you to create new book(record)s with the book class.