public function actionUpdateThumbnail() { $form = new FileUploadModel(); $form->setScenario(FileUploadModel::SCENARIO_IMAGE); if (\Yii::$app->request->isPost) { $form->uploadedFile = UploadedFile::getInstance($form, 'uploadedFile'); } if (!$form->validate()) { $ex = new ValidationException(); $ex->setData($form->errors); throw $ex; } else { $form->uploadedFile->saveAs('assets/thumbnail.' . $form->uploadedFile->extension); } return []; }