Souke/common/helpers/Upload.php

<?php

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namespace common\helpers;

use yii\web\UploadedFile;

class Upload {

    public static function uploadFile($model, $champs, $filename_old = '') {
        $file = UploadedFile::getInstance($model, $champs);
        if ($file) {
            $file_name = $file->baseName . '-' . uniqid() . '.' . $file->extension;
            $file->saveAs('../../frontend/web/uploads/' . $file_name);
            $model->$champs = $file_name;
        } else {
            $model->$champs = $filename_old;
        }

        $model->save();
    }

}