code: public function getViewersLinkedToDbColumns($includeViewersForRelations = false) {
          $ret = [];
          foreach ($this->getValueViewers() as $key => $viewer) {
              if ($viewer->isLinkedToDbColumn() && ($includeViewersForRelations || !$viewer->hasRelation())) {
                  $ret[$key] = $viewer;
              }
          }
          return $ret;
      }
docs: Get only viewers that are linked to table columns defined in TableConfig class ($valueViewer->isDbColumn() === true)
  @param bool $includeViewersForRelations - false: only vievers linked to main table's columns will be returned
  @return AbstractValueViewer[]|DataGridColumn[]|FormInput[]|ValueCell[]