/**
  *
  */
 public function init()
 {
     parent::init();
     if ($this->modelClass === null) {
         $this->modelClass = Category::className();
     }
 }
 /**
  * @return \yii\db\ActiveQuery
  */
 public function getCategory()
 {
     return $this->hasOne(Category::className(), ['id' => 'child_id']);
 }