如何在原则2中将实体重新保存为另一行

Try cloning and add the following method to your entity

public function __clone() {
$this->id = null;
}

You may need to detach the entity before persisting it. I don't have my dev machine handy to test this right now.

$f = clone $e;
$em->detach($f);
$em->persist($f);
$em->flush();

Update

Just tried using a simple SQLite demo. You shouldn't need to do anything. The following worked for me without adding a __clone() method or doing anything else out of the ordinary

$new = clone $old;
$em->persist($new);
$em->flush();

Once flushed, the $new entity had a new ID and was saved as a new row in the DB.

I would still null the ID property via the __clone() method as it makes sense from a pure model view.

Update 2

Digging into the Doctrine code, this is because the generated proxy classes implement __clone() with this important line

unset($this->_entityPersister, $this->_identifier);

I just do:

/**
* __clone
*
* @return void
*/
public function __clone()
{
$this->id = null;
}

More details here https://www.doctrine-project.org/projects/doctrine-orm/en/2.7/cookbook/implementing-wakeup-or-clone.html

Copying the data in a new Object of the same class and persisting it will do. Keep it simple!