Keeping object consistence at its creation

Question

Let's assume I have 2 objects Product and Volume. 1 Product must have at least 1 Volume which means: Product ----> 1...* Volume.

I want to keep the consistence of Product at its creation, in other words, I want to block the user to create products without any volumes.

I have a ready working code, but nonetheless I want to know your opinions guys.

Here is the running code: https://3v4l.org/t7JqO#v700

Here is my code:

<?php
declare(strict_types = 1);
namespace App
{
 class Product
 {
 private $id;
 private $name;
 private $volumes;
 /**
 * Product constructor.
 * @param int $id
 * @param string $name
 * @param array $volumes
 * @throws \InvalidArgumentException
 */
 public function __construct(int $id, string $name, array $volumes)
 {
 $this->id = $id;
 $this->name = $name;
 if (count($volumes) === 0) {
 throw new \InvalidArgumentException('Your product must have 1 product at least.');
 }
 $this->volumes = $this->prepareVolumes($volumes);
 }
 private function prepareVolumes(array $volumes)
 {
 foreach ($volumes as $volume) {
 $volume->setProduct($this);
 }
 return $volumes;
 }
 }
 class Volume
 {
 protected $id;
 protected $product;
 protected $description;
 public function __construct(string $description)
 {
 $this->description = $description;
 }
 public function setProduct(Product $product)
 {
 $this->product = $product;
 }
 }
 class ProductTest
 {
 public function __construct()
 {
 $volume1 = new Volume('part-1');
 $volume2 = new Volume('part-2');
 $volume3 = new Volume('part-3');
 $product = new Product(1, 'BED', [$volume1, $volume2, $volume3]);
 $invalidProduct = new Product(2, 'Table', []);
 }
 }
 return new ProductTest();
}

Answer 1

At first:

Note: Strict typing is only defined for scalar type declarations, and as such, requires PHP 7.0.0 or later, as scalar type declarations were added in that version.

Secondly:
You are passing in an array of volumes $volumes to the __construct function when instantiating an object of class Product. But there is no confidence that each element of $volumes is an object of Volume class. Someone could put into $volumes array an arbitrary value.
I would recommend applying dependency with Volume class and pass in Product constructor only one object of Volume class (following the initial rule: "Product must have at least 1 Volume"). And then, if necessary, you will be able to add some additional 'volumes' to product object using an auxiliary method addVolume().
See the optimized version:

<?php
declare(strict_types = 1);
namespace App
{
 class Product
 {
 private $id;
 private $name;
 private $volumes = [];
 /**
 * Product constructor.
 * @param int $id
 * @param string $name
 * @param array $volumes
 */
 public function __construct(int $id, string $name, Volume $volume)
 {
 $this->id = $id;
 $this->name = $name;
 $volume->setProduct($this); 
 $this->volumes[] = $volume;
 }
 public function addVolume(Volume $volume)
 { 
 $volume->setProduct($this); 
 $this->volumes[] = $volume;
 }
 }
 class Volume
 {
 protected $id;
 protected $product;
 protected $description;
 public function __construct(string $description)
 {
 $this->description = $description;
 }
 public function setProduct(Product $product)
 {
 $this->product = $product;
 }
 }
 class ProductTest
 {
 public function __construct()
 {
 $volume1 = new Volume('part-1');
 $volume2 = new Volume('part-2');
 $volume3 = new Volume('part-3');
 $product = new Product(1, 'BED', $volume1);
 $product->addVolume($volume2);
 $product->addVolume($volume3);
 $invalidProduct = new Product(2, 'Table', []);
 }
 }
 return new ProductTest();
}

• Daniel Lima: Great solution @romanperekhrest. I had already got the point about confidence tip and in my production code I'm using an collection instead of array. Thank you. I owe you a beer.