gistfile1.php

public function hookBeforeBundleInsert(&$args){
    $item = $args["instance"];
    $vn_type_id = $item->get($item->getTypeFieldName());
    $va_type_list =  $item->getTypeList(array("directChildrenOnly" => false, 'returnHierarchyLevels' => true, 'item_id' => null));
    $type = $va_type_list[$vn_type_id];

    if($type["idno"] === "copy") {
        //preferred_label = shelf mark
        $preferredLabel = $item->get("ca_objects.preferred_labels"); //returns empty string
        $barcode = $item->get("ca_objects.barcode");                 //returns empty string
        $sourceId = $item->get("ca_objects.source_id");              //returns id
        $relatedItems = $item->get("ca_objects.related.object_id");  //returns empty string

        //generate shelf mark                 -> $autoShelfMark
        //select source depending on bar code -> $newSourceId
        
        $item->set("preferred_labels.name", $autoShelfMark);
        $item->set("source_id", $newSourceId);

        //Test if values are set
        $preferredLabelNew = $item->get("ca_objects.preferred_labels"); //returns empty string
        $sourceIdNew = $item->get("ca_objects.source_id");              //returns $newSourceId
    }
}