Пример простого кода.

<?php

namespace App\DataFixtures;

use App\Entity\Product;
use App\Entity\Shipment;
use Doctrine\Bundle\FixturesBundle\Fixture;
use Doctrine\Common\DataFixtures\DependentFixtureInterface;
use Doctrine\Common\Persistence\ObjectManager;

class ProductFixtures extends Fixture
{
	public function load(ObjectManager $manager)
	{
		for ($i = 0; $i < 50; $i++) {
			$product = new Product();
			$product->setName('product '.$i);
			$product->setPrice(mt_rand(10, 100));
			$product->setQty(mt_rand(1, 10));
			$manager->persist($product);
		}
		$manager->flush();
	}
		
}