Symfony2和Doctrine2：Command循环在每个循环中创建新实体

I have a Symfony2 CLI script running which should update a timestamp each 3 seconds. The problem is: $this->em->persist($processInfo) creates a new entry in the DB each time it is executed. I want it to UPDATE, not to CREATE on each cycle.

$processInfo = new ....ProcessInfo();

while(true){
     $someObject = new ..();
     $this->em()->persist($someObject);

     $this->em()->clear(); // sorry forgot this line in my initial question

     $processInfo->setLastCheckOn($now); // to know if the script is still running, we set a timestamp in the db
     $this->em()->persist($processInfo);
     $this->em()->flush();


     sleep(3);
}

any ideas?

Use persist only once. Then you need to commit the active transaction and start a new , in order to tell the database to save them and make a new transaction:

$processInfo = new ....ProcessInfo();
$this->em()->persist($processInfo);
$this->em()->getConnection()->commit();
while(true){
    $processInfo->setLastCheckOn($now); // to know if the script is still running, we set a timestamp in the db
    $this->em()->flush();
    sleep(3);
}