PHP Extend class which can only be constructed through static method which calls new static()

Question

I have this class Product with a few properties like Name, Description etc. An object of class Product can only be created through a static method fromArray()

$product = Product::fromArray($arr);


class Product 
{
    // getters and setters
    ...

    public static function fromArray($productArr) {
        $productObj = new static();

        if (isset($productArr['ProductId'])) {
            $productObj->setProductId($productArr['ProductId'];
        } else {
            $productObj->setProductId(null)
        }
        if (isset($productArr['Name'])) {
            $productObj->setName($productArr['Name'];
        } else {
            $productObj->setName(null)
        }
        ...

        return $productObj;
    }
}

I now have a class ProductVariant, (containing extra information like size and/or colour for a product) which should extend this class. If I simply do parent::fromArray($productVariantArr) in this class' fromArray() method I will end up with an object of type Product and not of type ProductVariant, which is obviously not what I want.

So I found a way to work around this, but I am not convinced at all it is the right way to do it. This is what I did:

I changed the fromArray() method of Product to the following, making it possible to pass in an object of the extending class

public static function fromArray($productArr, $object = null) {
    if ($object !== null) {
        $productObj = $object;
    } else {
        $productObj = new static();  
    }
    ....
}

And the ProductVariant class

class ProductVariant extends Product 
{
    // getters and setters 
    ...

    public static function fromArray($productVariantArr, $object = null) {
        $productVariantObj = new static();
        $productVariantObj = parent::fromArray($productVariantArr, $productVariantObj);

        if (isset($productVariantArr['Size'])) {
            $productVariantObj->setSize($productVariantArr['Size']);
        } else {
            $productVariantObj->setSize(null);
        }
        ....

        return $productVariantObj;
    }
}

But as I said, this doesn't seem right. Any help on how to extend the Product class is very welcome

Answer 1

How about making the fromArray method pretty simple and generalized, so that it could be used in all the child classes easily in an abstract way.

 class Product
 {

     ...

     public static function fromArray(array $attrs)
     {
         $instance = new static();

         foreach($attrs as $key => $value) {
             $setter = 'set'.$key;

             // Check if the setter method exists
             if (method_exists($instance, $setter)) {
                 // Invoke that method dynamically
                 call_user_func(array($instance, $setter), $value);
             } else {
                 // You might want to throw an exception here
             }
         }

         return $instance;
     }
 }

 // Child class
 class ProductVariant extends Product
 {
     ...     
 }

Now, just do this:

 // Now create instances
 $product = Product::fromArray([
     'Name' => 'something',
     'ProductId' => 234
 ]);

 $productVariant = ProductVariant::fromArray([
     'Size' => '15px',
     'Zier' => null
 ]);

 print_r($product);
 print_r($productVariant);

Hope, this solves your problem. Not sure, what exactly you are looking for.