Save huge array to database - sql

Question

First the introduction, in case there's is a better approach: I have a product table with *product_id* and stock, where stock can be as big as 5000 or 10000, I need to create a list (in another table) where I have a row for each item, this is, if a *propduct_id* has stock 1000 I'll have 1000 rows with this *product_id*, and plus, this list needs to be random.
I chose a PHP (symfony2) solution, as I found how to get a random single product_id based on stock or even how to random order the product list, but I didn't find how to "multiply" this rows by stock.
Now, the main problem:
So, in PHP it's no so difficult, get product_id list, "multiply" by stock and shuffle, the problem comes when I want to save:
If I use $em->flush every 100 records or more I get a memory overflow after a while
If I use $em->flush in every record it takes ages to save
This is my code to save which maybe you can improve:
foreach ($huge_random_list as $indice => $id_product)
{
$preasignacion = new ListaPreasignacion();
$preasignacion->setProductId($id_product);
$preasignacion->setOrden($indice+1);
$em->persist($preasignacion);
if ($indice % 100 == 0) $em->flush();
}
$em->flush();
Edit with final solution based on #Pazi suggestion:
$conn = $em->getConnection();
foreach ($huge_random_list as $indice => $id_product)
{
$conn->executeUpdate("insert into product_list(product_id, order) "
." values({$id_product}, {$indice})");
}

Answer 1

I would suggest to abstain from doctrine ORM and use the DBAL connection an pure sql queries for this purpose. I do this always in my applications, where I have to store much data in short time. Doctrine adds too much overhead with objects, checks and dehydrating. You can retrieve the DBAL connection via the DI container. For example in a contoller:
conn = $this->get('database_connection');
Read more about DBAL