Doctrine\ORM\UnitOfWork::computeAssociationChanges PHP Method

    private function computeAssociationChanges($assoc, $value)
    {
        if ($value instanceof PersistentCollection && $value->isDirty()) {
            if ($assoc['isOwningSide']) {
                $this->collectionUpdates[] = $value;
            }
            $this->visitedCollections[] = $value;
        }

        // Look through the entities, and in any of their associations, for transient (new)
        // enities, recursively. ("Persistence by reachability")
        if ($assoc['type'] & ClassMetadata::TO_ONE) {
            if ($value instanceof Proxy && ! $value->__isInitialized__) {
                return; // Ignore uninitialized proxy objects
            }
            $value = array($value);
        } else if ($value instanceof PersistentCollection) {
            // Unwrap. Uninitialized collections will simply be empty.
            $value = $value->unwrap();
        }

        $targetClass = $this->em->getClassMetadata($assoc['targetEntity']);
        foreach ($value as $entry) {
            $state = $this->getEntityState($entry, self::STATE_NEW);
            $oid = spl_object_hash($entry);
            if ($state == self::STATE_NEW) {
                if ( ! $assoc['isCascadePersist']) {
                    throw new InvalidArgumentException("A new entity was found through a relationship that was not"
                            . " configured to cascade persist operations: " . self::objToStr($entry) . "."
                            . " Explicitly persist the new entity or configure cascading persist operations"
                            . " on the relationship.");
                }
                $this->persistNew($targetClass, $entry);
                $this->computeChangeSet($targetClass, $entry);
            } else if ($state == self::STATE_REMOVED) {
                return new InvalidArgumentException("Removed entity detected during flush: "
                        . self::objToStr($entry).". Remove deleted entities from associations.");
            } else if ($state == self::STATE_DETACHED) {
                // Can actually not happen right now as we assume STATE_NEW,
                // so the exception will be raised from the DBAL layer (constraint violation).
                throw new InvalidArgumentException("A detached entity was found through a "
                        . "relationship during cascading a persist operation.");
            }
            // MANAGED associated entities are already taken into account
            // during changeset calculation anyway, since they are in the identity map.
        }
    }