[TYPO3-mvc] How to compare a DateTime object correctly in an Extbase query?

[Jan Kornblum]

Dear newsgroup,

i've to compare a DateTime property in a repository query to implement 
a "previous" / "next" navigation for a single view. What should the 
query look like correctly? This is what i've done so far:

public function findPrevious(\Vendor\Ext\Domain\Model\Post $post) {
	$query = $this->createQuery();
	$query->setOrderings(array('datePublished' => 
\TYPO3\CMS\Extbase\Persistence\QueryInterface::ORDER_ASCENDING));
	$query->matching($query->greaterThan('datePublished', 
$post->getDatePublished()->format('Y-m-d H:i:s')));
	$previousPost = $query->execute()->getFirst();
	return $previousPost;
}

public function findNext(\Vendor\Ext\Domain\Model\Post $post) {
	$query = $this->createQuery();
	$query->setOrderings(array('datePublished' => 
\TYPO3\CMS\Extbase\Persistence\QueryInterface::ORDER_DESCENDING));
	$query->matching($query->lessThan('datePublished', 
$post->getDatePublished()->format('Y-m-d 00:00:00')));
	$nextPost = $query->execute()->getFirst();
	return $nextPost;
}

But it only works when i use "->format('Y-m-d 00:00:00')" on the 
DateTime object in the second query. Which "format" must be used to get 
an exact comparison?

Kind regards, Jan