gistfile1.php

<?php

$user = new User();

$user->addComment(new Comment('foo'));
$user->addComment(new Comment('baz'));
$user->addComment(new Comment('bar'));

$em->persist($user); // i only want the "user" object to be persisted, not the whole object graph
$em->flush();

It results in the error of comment #2

but comment doesnt have identity through a foreign entity, it has its own ID field with auto generated value. You must show the wrong code, you cannot get that error message.

I think you've just answered my question. In "the real code", the entity has identity through a foreign entity.

I have the same problem, did you find a solution to the problem?