/**
  * @return ActiveQuery
  */
 public function getTopics()
 {
     return $this->hasMany(TopicModels::className(), ['forum_id' => 'id'])->inverseOf('forum');
 }
 /**
  * @return ActiveQuery
  */
 public function getTopic()
 {
     return $this->hasOne(TopicModels::className(), ['id' => 'topic_id']);
 }