public function tableContent($fields, $instance)
    {
        $output = '';
        foreach ($fields as $f) {
            if ($this->isIdField($f)) {
                $related = $this->getRelatedField($f);
                $relation = $instance->$related;
                $field = $this->getPrimaryField($relation);
                if (strpos($field, ',')) {
                    $subfields = explode(',', $field);
                    $display = '';
                    foreach ($subfields as $sf) {
                        $display .= $relation->$sf.' ';
                    }
                } else {
                    $display = $relation->$field;
                }
                $output .= '<td>'.$display.'</td>';
            } else {
                $output .= '<td>'.$instance->$f.'</td>';
            }
        }

        return $output;
    }