[TYPO3-mvc] fe_users->getUsergroup() is empty

[Martin Ernst]

Hello,

I have extended the fe_users table in my extension with a customer 
object model. I want to get the usergroup(s) by $this->getUsergroup() in 
that model.

Whatever I do and regardless of the number of FE usergroups a customer 
is in (in fact each customer is in at least 1 group), the usergroups 
ObjectStorage I get is always empty.

The getter looks like

	public function isTest(){
		$groups = $this->getUsergroup();
		...
	}

$groups->count() is always 0 while $this->getUsername() gets the correct 
username.

Any hints very welcome.
Martin