Guys,
I have this code on my update section of CRUD.
Everything worked fine but now it insert new record instead of update the existing one.
$model = Yii::createObject(['class' => $modelClassName]);
$model = $model->findOne($id);
if($id === null || $model === null)
throw new \yii\web\HttpException('404');
if($model->load($_POST) && $model->save()){
Yii::$app->session->setFlash('success', 'Saved');
$model = Yii::createObject(['class' => $modelClassName]);
}