FRONTEND_MVC/models/TopicImages.php

<?php

namespace app\models;

use app\models\base\NewsTopic;
use Yii;

/**
 * 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
 * @property NewsTopic $topic
 */
class TopicImages extends \yii\db\ActiveRecord
{
    /**
     * {@inheritdoc}
     */
    public static function tableName()
    {
        return 'topic_images';
    }

    /**
     * {@inheritdoc}
     */
    public function rules()
    {
        return [
            [['topic_id'], 'integer'],
            [['uploaded_at'], 'safe'],
            [['alt','ext'], 'string'],
        ];
    }

    /**
     * {@inheritdoc}
     */
    public function attributeLabels()
    {
        return [
            'id' => 'ID',
            'topic_id' => 'Topic ID',
            'uploaded_at' => 'Uploaded At',
            'alt' => 'Alt',
        ];
    }

    public function getTopic(){
        return $this->hasOne(NewsTopic::class,["id"=>"topic_id"]);
    }

    public function getUrl(){
        return "/topic-images/{$this->topic_id}/{$this->id}.{$this->ext}";
    }
}