code: public function getViewersForRelations() {
          $ret = [];
          foreach ($this->getValueViewers() as $key => $viewer) {
              if ($viewer->isLinkedToDbColumn() && $viewer->hasRelation()) {
                  $ret[$key] = $viewer;
              }
          }
          return $ret;
      }
docs: Get only viewers that are linked to main table's relation
  @return AbstractValueViewer[]|DataGridColumn[]|ValueCell[]|FormInput[]