在哪里放置功能？ 在实体或服务？

I have entity that can be archived. All data from current object is copied to new archive object and current object is deleted. Now it is realized in entity:

class Entity
{
...
    public function archive($em)
    {
        $objectArchive = new EntityArchive($this->toArray()); // all archive object properties are set in constructor
        $em->persist($objectArchive);

        $em->remove($this);

        return $objectArchive;
    }
...
}

Recently I've read that functions that modify more than one entity should be placed in services and now I'm confused. Should I move this function to service? Something like this:

class ServiceEntityArchiver
{
    private $em;

    public function __construct($em)
    {
        $this->em = $em;
    }

    public function archive($object)
    {
            $objectArchive = new EntityArchive($object->toArray());
            $this->em->persist($objectArchive);

            $this->em->remove($object);

            return $objectArchive;
    }
}

What do you think about this?