FRONTEND_MVC/models/BasicImage.php

<?php

namespace app\models;

use yii\base\Model;

/**
 * This is the model class for table "topic_images".
 *
 * @property int $id
 * @property int|null $topic_id
 * @property string|null $uploaded_at
 * @property string|null $alt
 * @property string|null $ext
 */

class BasicImage extends Model
{
    public $topic_id = NULL;
    const SIZE_HD = "_size1";
    const SIZE_SD = "_size2";
    const SIZE_SD_16_9 = "_size2";
    const SIZE_LQ = "_size4";

    public function getUrl($size = self::SIZE_HD){
        return "";
    }
}