/**
  * @return \yii\db\ActiveQuery
  */
 public function getFile()
 {
     return $this->hasOne(Files::className(), ['file_id' => 'file_id']);
 }
 /**
  * @return \yii\db\ActiveQuery
  */
 public function getFiles()
 {
     return $this->hasMany(Files::className(), ['folder_id' => 'folder_id']);
 }