Doctrine query builder ~ datetime - php

Question

I'm trying to create a simple chatbox in symfony2 / doctrine 2.
For testing I'm checking for new messages every 5 seconds, so in my query I try to get all messages by getting all messages with a datetime greater than the current one minus 5 seconds.
I try to do so the following way, but it returns all messages in the database instead of the ones posted in the last 5 seconds
$em = $this->getDoctrine()->getManager();
$qb = $em->createQueryBuilder();
$qb->select('m')
->from('ChatboxBundle:ChatMessage', 'm')
->where(':new > :last')
->setParameter('new', 'm.postdate' )
->setParameter('last', new \DateTime('-5 second'), \Doctrine\DBAL\Types\Type::DATETIME);
$updatedata = $qb->getQuery()->getResult();
Any ideas on what I'm doing wrong?

Answer 1

m.postdate is a field name and therefore shouldn't be passed in as a parameter. Try this
$qb = $em->createQueryBuilder();
$qb->select('m')
->from('ChatboxBundle:ChatMessage', 'm')
->where('m.postdate > :last')
->setParameter('last', new \DateTime('-5 second'), \Doctrine\DBAL\Types\Type::DATETIME);
$updatedata = $qb->getQuery()->getResult();

Answer 2

Note thats You don't need to use \Doctrine\DBAL\Types\Type::DATETIME
The doc say :
Calling setParameter() automatically infers which type you are setting as value. This works for integers, arrays of strings/integers, DateTime instances and for managed entities. If you want to set a type explicitly you can call the third argument to setParameter() explicitly. It accepts either a PDO type or a DBAL Type name for conversion.