yii2 file upload

if ($model->load(Yii::$app->request->post())){
            $image = UploadedFile::getInstance($model, 'image_file');
            $fileext=time();
            $image->saveAs('uploads/' . $fileext.$image->baseName . '.' . $image->extension);
            $model->image_file = $fileext.$image->baseName.'.'.$image->extension;
            $model->save();
            return $this->redirect(['view', 'id' => $model->id]);
        }
        else{
            return $this->render('create', [
                'model' => $model,
            ]);
        }