Adding Assets to a Domain Model


I’m trying to add Assets (PDFs …) to a model:
The following method is located in our MemberServive. A Member is a user, that can log in.
The method below is called by a CommandController.

Property and methods (add, set, remove) concerning Assets, I copied from AssetCollection.
I configured a dedicated storage ‘member’.
There is no error:
The Resource and the Asset are created in the DB.
PROBLEM: The Join-Table member_asset keeps empty:

 * @param integer $memberNumber
 * @param string $filename
 * @return array
public function addAssetFromFile( $memberNumber, $filename )
     * resource aus file erzeugen und im eigenen storage speichern
     * @var Resource $resource
    $resource = $this->resourceManager->importResource( $filename, self::RESOURCE_COLLECTION_FOR_MEMBERS );

     * @var Asset $asset
    $asset = new Asset($resource);
    $assetRepo = $this->assetService->getRepository($asset);

     * @var Member $member
    $member = $this->memberRepository->findOneByMemberNumber($memberNumber);

The definition of the Asset property in the Domain Model Member:

 * @var Collection<\TYPO3\Media\Domain\Model\Asset>
 * @ORM\ManyToMany(inversedBy="assetCollections", cascade={"persist"})
 * @Flow\Lazy
protected $assets;

I think here is the problem:
The inversedBy is definitively wrong (copy and paste).
I don’t want to modify the generic class Asset.
So: inversedBy WHAT??

It would be perfectly OK to me to have a single side OneToMany relation, or so.
One Member can have many documents (Assets). One Document belongs exactly to one member. (Like an invoice).

My collection is not ‘persist’, but ‘member’.
Should I use ’ cascade={“member”}’

One more remark:
I use class table inheritance here. Member ist the parent, personalMember and CorporateMember extend Member.

I hope somebody can advice me.