PHP Object : Loop on product list

Question

I have a quick one: I'm a beginner with PHP Object, and I have a product table with all my products.

I also have a class for my product (with a constructor that fills my instance with all the parameters of my product).

Say I want a list of all my product, shall I create a separate class for my list of products, or create a function that creates a new instance of my product class ?

I don't really get the benefits of it right now, because if I have to execute the exact same query as my class query, it's useless ?

Thank's for your tips !

UPDATE

Thank's folks ! It's still quite complicated for me, but here's what I did (talking about books) trying to follow your advices.

I created a DAO. Inside this DAO, I have two static functions that return me either a list of books or a single book, and one static that creates the book object.

With this method, I still have 2 queries (one for the list, one for the single book). I have a feeling this is wrong but any help is appreciated :)

class bookDAO {

    public static function getBooks() {
        $books = array();
        $db = databaseConnection::getInstance();
        $query = $db->query("SELECT * FROM books");
        while($row = $query->fetchObject()) {
            $book = self::createBookFromRow($row);
            $books[] = $book;
        }
        return $books;
    }

    public static function getBook($id){
        $db = databaseConnection::getInstance();
        $query = $db->prepare("SELECT * FROM books WHERE id=:id");
        $query->execute(array(":id"=>$id));
        $row = $query->fetchObject();
        $book = self::createBookFromRow($row);
        return $book;
    }

    private static function createBookFromRow($row) {
        $book = new book($row);
        return $book;
    }

}

Answer 1

It's common to create an array of objects in this case.

For example:

$products = array();
foreach($results as $result) {
  $products[] = new Product($result);
}
print_r($products);

Answer 2

Your Product class is not suppose to execute any query, separate that into a DAO e.g. ProductDAO class

class ProductDAO
{
  function static getProducts()
  {
     //Your query here: PDO, MySQLi, MySQL etc
    $products = array(); //to store array of products

    while($row = mysql_fetch_assoc($result))
    {
       $product = createProductFromRow($row);

       $products[] = $product;
    }

    return $products;
}

   private static function createProductFromRow($row)
   {
   $product = new Product();
   $product->setId($row["id"]);
   $product->setName($row["Name"]);
   //etc

   return $product; 
   }
}

From your page

  $products = ProductDAO::getProducts();

  foreach($products as $p)
  {
     echo ($p->getName() + '<br />');
  }

Answer 3

You could simply add an array. Or if you want to add some methods to the productslist you could implement something like the following:

class Products
{
    private $productFactory;

    private $products = array();

    public function __construct(ProductFactory $productFactory) {
        $this->productFactory = $productFactory;
    }

    public function addProduct($product)
    {
        $this->products[] = $this->productFactory->build($product);
    }

    public function addProducts($products)
    {
        foreach ($products as $product) {
            $this->addProduct($product);
        }
    }

    // do soemthing with all products
    public function changeProducts()
    {
        foreach($this->products as $product) {
            $product->changeSpec('new spec value');
        }
    }
}

class Product
{
    private $someSpec;

    public function __construct($spec)
    {
        $this->someSpec = $spec;
    }

    public function changeSpec($spec) {
        $this->someSpec = $spec;
    }
}

class ProductFactory
{
    public function build($spec) {
        return new Product($spec);
    }
}

// build the productslist object
$productFactory = new ProductFactory();
$products = new Products($productFactory);
$products->addProducts(array(
    'some spec of product1',
    'some spec of product2',
));

note that I manually add products, but this may as well be a recordset from some persistent storage mechanism (e.g. a db). Or perhaps better inject some class which accesses the database to retrieve the products. Don´t do any queries inside the Product / Products classes. If you do you are tightly coupling something (the database) which makes it very hard to test. And besides that you also violate SRP.

Note that I have created a factory to create new instances of the Product class. This way you haven't tightly coupled the Product class to the Products class. This makes it far more easier to mock the Product class in case you want to do unit testing.

UPDATE

Another thing you could do with the Products class is let it implement Iterator interface so you could also loop through the products if you want.

Answer 4

Products class where all Product references will be saved

class Products {

    static private $store = array();

    static public function save(Product $object)
    {
        self::$store[] = $object;
    }

    static public function getAll()
    {
        return self::$store;
    }

}

Save every Product reference to the Products class

The easiest way is to do it in your Product constructor.

# your Product class
class Product {

    public function __construct()
    {
        # your stuff here..

        # save reference of current Product to the Products
        Products::save($this);
    }

}

Your initialization of the products

This is just for test, use your logic here to initialize the Product objects.

new Product;
new Product;
new Product;

Loop through all products

foreach (Products::getAll() as $product) {
    var_dump($product);
}