Import CSV file to Database using Yii2 - php

Question

I'm trying to import CSV file to the database using yii2 framework.
Controller
public function actionIndex($message=””)
{
// $model = new ProjectDocument;
//error_reporting(E_ALL);
//ini_set('display_error', 1);
$model = new ProjectDocument();
if ($model->load(Yii::$app->request->post()) ) {
$model->file = UploadedFile::getInstance($model, 'file');
// if ($model->load(Yii::$app->request->post())){
// $filename = 'Data.' . $file->extension;
$upload = $file->saveAs('uploads/' . $filename);
if ($upload) {
define('CSV_PATH', 'uploads/');
$csv_file = CSV_PATH . $filename;
$filecsv = file($csv_file);
foreach ($filecsv as $data) {
$title = _file[1];
$description = $file[2];
$phase = $file[3];
$modelnew->title = $title;
$modelnew->description = $description;
$modelnew->phase = $phase;
$modelnew->save();
}
unlink('uploads/'.$filename);
return $this->render('create',array('model'=>$model, 'message'=>$message));
}
}else{
return $this->render('create',array('model'=>$model, 'message'=>$message
));
}
return $this->render('create',array('model'=>$model, 'message'=>$message
));
}
But I getting an error like this,
"Access to undeclared static property: Yii::$app"
Anyone can help me to rectify the error, Thank you in advance..