code: private function resolveDisplayField() {
          $result = null;
  
          $columns = $this->model->getColumns();
          foreach ($columns as $column) {
              if ($column->getType() == Type::STRING && in_array($column->getName(), $this->displayFieldNames)) {
                  $result = $column->getName();
              }
          }
  
          if ($result == null) {
              /* If we couldn't find a display field, just return the first one */
              $result = empty($columns) ? '' : $columns[0]->getName();
          }
  
          return $result;
      }
docs: Tries to resolve the display field for the Model.
  The possible column names are defined in $displayFieldNames.
  
  @return String the name of the column to use as display field.