[TYPO3-mvc] Problems with loading an object from database

[Ephraim Härer]

Hello,
in my first Extbase-extension I could load an object from database like 
this:

if ($this->request->hasArgument('key')){
	$thekey = $this->request->getArgument('key',$key);
	$check = new Tx_Myextension_Domain_Model_Entries;
	$check = $this->entriesRepository->findOneByChangekey($thekey);
}

And then for example:
$check->setName('New Name');

But now I created a new extension with the extension builder and this 
code doesn't work now.

What's wrong? Anybody an idea?

-- 
Mit freundlichen Grüßen
Ephraim Härer