A new entity was found through the relationship - Doctrine - doctrine-orm

Question

I have a cached entity Product. I retrieve the entity and update some properties including adding price into it.
Relationship is set up like this
class Product
{
/**
* #var ArrayCollection
*
* #ORM\OneToMany(targetEntity="Price", mappedBy="product", fetch="EXTRA_LAZY")
*/
private $prices;
}
class Price
{
/**
* #var Product
*
* #ORM\ManyToOne(targetEntity="Product", inversedBy="prices")
* #ORM\JoinColumn(name="product_id", referencedColumnName="id")
*/
private $product;
}
I am trying to save properties like this.
// Here $em is Entity Manager
$cacheDriver = $em->getConfiguration()->getResultCacheImpl();
$product = $cacheDriver->fetch($key)
$product->setUpdatedAt(new \DateTime());
$price = new Price;
$label = $em->getReference(PriceLabelEntity::class, $labelId);
$price->setLabel($label)
->setPriceLabelId($labelId)
->setProduct($productEntity)
->setProductId($product->getId());
$em->persist($price);
$product->addPrice($price);
$em->flush();
But whenever I do that I get the exception saying.
A new entity was found through the relationship 'Price#product' that was not
configured to cascade persist operations for entity:
Product#0000000043c0cdc400007fec6b41ca76. To solve this issue: Either
explicitly call EntityManager#persist() on this unknown entity or configure
cascade persist this association in the mapping for example
#ManyToOne(..,cascade={"persist"}). If you cannot find out which entity
causes the problem implement 'Product#__toString()' to get a clue.
Even more strange issue if I do just this.
$product->setUpdatedAt($timeStamp);
$em->flush();
It does not throw any error but no data is saved in DB. Not sure whether this issues are related or not either.
I tried to put cascade too but it gives different error. Is there any way to resolve this issue.

Answer 1

It is my understanding that Doctrine entity managers are fairly adept (at least, one would hope) at managing their result cache, so fiddling with it directly may be the issue.
Instead of hitting the result cache directly, try using:
$product = $entityManager->find('Product',$key);
Then, you also seem to have a typo on the last line - missing an "e" in "entityManager" - but I am sure that would throw an error, so it's probably a copy/paste issue when creating this question.
EDIT: You are also using both $product and $productEntity. If these are meant to be the same variable, you should pick one name and stick with it.

Answer 2

#Rushing thank you very much for your reply. You are right there are some typos because I had to do some changes in code to paste in StackOverflow but the actual code is correct. I am sorry I was bit late to reply on this topic. The solution you provided was good but even better solution was to use merge like this.
$productEntity = $em->merge($productEntity);
....rest of the logic
In this way we did not have to query the database again and entity was fresh.