Doctrine inserts twice when adding one related entity and using $em->clear() - symfony

Question

When I try to add new info item it either inserts two of them or none. In the state of code below it inserts two. If i comment something it inserts none. When I comment the line with $em->clear() it inserts exactly one, as I need it. What I don't understand and what I'm doing wrong?
$limit = 10;
$offset = 0;
do {
$products = $selectedModelQuery->getQuery()
->setFirstResult($limit * $offset)
->setMaxResults($limit)->getResult();
$offset++;
$count = count($products);
/** #var \Nti\ApiBundle\Entity\Product $product */
foreach ($selectedModelQuery->getQuery()->getResult() as $product) {
if (!$product->getCollections()->contains($productCollection)) {
$product->addCollection($productCollection);
$productInfo = new ProductInfo;
$productInfo->setProduct($product);
$productInfo->setData($productCollection->getMessage());
$productInfo->setInfoType(ProductInfoInterface::TYPE_CUSTOM);
//$em->merge($product);
//$em->persist($productInfo);
}
}
$em->flush();
$em->clear();
} while ($count);
Main Entity:
class Product {
/**
* #ORM\OneToMany(targetEntity="ProductInfo", mappedBy="product", cascade={"persist", "remove"})
* #var ProductInfoInterface[]|ArrayCollection
*/
protected $infoList;
....
}
Related Entity:
class ProductInfo {
/**
* #ORM\ManyToOne(targetEntity="\Nti\ApiBundle\Entity\Product", inversedBy="infoList")
* #ORM\JoinColumn(name="product_id", referencedColumnName="id", onDelete="CASCADE", nullable=false)
*/
protected $product;
...
}

Answer 1

Doctrine is based on Identity Map that keeps reference to all handled object (ie.: if you try to query two times for the same record by id, first time you hit the db but the second not and object is loaded from Identity Map).
When you use $em->clear() you are "discarding" all objects into Identity Map so, next iteration of do ... while will result in a brand new object (from ORM point of view) that will be flagged for writing operation.