public static function getFields() { return ['category' => ['class' => ForeignField::className(), 'modelClass' => BookCategory::className(), 'null' => true, 'editable' => false], 'category_new' => ['class' => ForeignField::className(), 'modelClass' => BookCategory::className(), 'null' => true, 'relatedName' => 'categories', 'editable' => false]]; }