symfony - Symfony2 Doctrine merge

Question

I am studying https://www.doctrine-project.org/projects/doctrine-orm/en/2.6/reference/working-with-associations.html but I cannot figure out what cascade merge does. I have seen elsewhere that

$new_object = $em->merge($object); 

basically creates a new managed object based on $object. Is that correct?

Answer 1

$em->merge() is used to take an Entity which has been taken out of the context of the entity manager and 'reattach it'.

• If the Entity was never managed, merge is equivalent to persist.
• If the Entity was detached, or serialized (put in a cache perhaps) then merge more or less looks up the id of the entity in the data store and then starts tracking any changes to the entity from that point on.

Cascading a merge extends this behavior to associated entities of the one you are merging. This means that changes are cascaded to the associations and not just the entity being merged.