How to validate relationships on object creation. ---> code execution: https://3v4l.org/t7JqO#v700

example-1.php

<?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();
}