ExtbaseObject with relation to multiple occurences of the same object - typo3

Question

I've got an ExtbaseObject with a relation that can contain multiple references to the same subobject.
I've extended the mm table for the relation with a uid field and set the option MM_hasUidField in the tca. In the backend everything works as intended:
But if I load the object in the frontend I get only one occurence of "Testzusatzpaket 1":
The tca configuration in question is:
'zusatzpakete' => [
'label' => 'LLL:EXT:ned_beratung/Resources/Private/Language/locallang_db.xlf:tx_nedberatung_domain_model_beratung.zusatzpakete',
'config' => [
'type' => 'select',
'renderType' => 'selectMultipleSideBySide',
'foreign_table' => 'tx_nedshop_domain_model_artikel',
'multiple' => true,
'maxitems' => 99,
'MM' => 'tx_nedberatung_beratung_zusatzpakete_mm',
'MM_hasUidField' => true,
],
],
In the model, the object is defined as an object storage:
/**
* zusatzpakete
*
* #var \TYPO3\CMS\Extbase\Persistence\ObjectStorage<\NED\NedShop\Domain\Model\Artikel>
* #cascade remove
*/
protected $zusatzpakete = null;
/**
* Adds a Zusatzpaket
*
* #param \NED\NedShop\Domain\Model\Artikel $zusatzpakete
* #return void
*/
public function addZusatzpakete(\NED\NedShop\Domain\Model\Artikel $zusatzpakete)
{
$this->zusatzpakete->attach($zusatzpakete);
}
/**
* Removes a Zusatzpakete
*
* #param \NED\NedShop\Domain\Model\Artikel $zusatzpaketeToRemove The Zusatzpakete to be removed
* #return void
*/
public function removeZusatzpakete(\NED\NedShop\Domain\Model\Artikel $zusatzpaketeToRemove)
{
$this->zusatzpakete->detach($zusatzpaketeToRemove);
}
/**
* Returns the Zusatzpakete
*
* #return \TYPO3\CMS\Extbase\Persistence\ObjectStorage<\NED\NedShop\Domain\Model\Artikel> $zusatzpakete
*/
public function getZusatzpakete()
{
return $this->zusatzpakete;
}
/**
* Sets the Zusatzpakete
*
* #param \TYPO3\CMS\Extbase\Persistence\ObjectStorage<\NED\NedShop\Domain\Model\Artikel> $zusatzpakete
* #return void
*/
public function setZusatzpakete(\TYPO3\CMS\Extbase\Persistence\ObjectStorage $zusatzpakete)
{
$this->zusatzpakete = $zusatzpakete;
}
Why does this not work in the frontend, what am I missing?

Answer 1

That's the way the Extbase ObjectStorage works. It retrieves the object hash of each object and uses this to only store objects uniquely. And the Extbase persistence ensures that every object is only created once by storing it in the persistence session after retrieval.
One option to bypass this is to promote your MM table to a 1st level table including TCA and an own domain model. This way each relation is a separate object and thus unique which allows you to have multiple relations to the same Artikel. And example of such a promoted MM table is the sys_file_reference table in TYPO3.
Your Beratung model would then have a multi-valued property (ObjectStorage) typed to the newly introduced relation model. That model then needs a property to represent the related Artikel.
If you do this you can still keep the field names in your MM table if you want to continue maintaining it with the current setup. Then you only need to change your model relations as described. However if you want to have more descriptive names in your table, you can rename the fields but then it cannot be managed as MM table in TYPO3 anymore so you'd need to change your base table field type e.g. to inline.
One final suggestion: it is general consensus to use English for everything in code including model and property names. This makes it a lot easier for others to get into your code and blends well with the English of the programming language.