这个报错，找不到原因·····

类的属性不存在:app\index\model\Topic->praises_count

public function detail(){
$topicId=input('get.id');
$topic=TopciModel::getTopic($topicId);
$user=session('user');
$this->assign([
'user'=>$user,
'topic'=>$topic,
'topicTags' => TopicTag::getTopicTagsByTopicId($topic->id),
'categoryNames' => getCategoryNames($topic->category_id),

]);
echo $this->fetch('detail');
}

class TopicTag extends Model{
public static function getTopicTagsByTopicId($topicId){
return self::where(['topic_id'=>$topicId])->select();
}

public function tag(){
return $this->belongsTo('Tag','tag_id');
}
}

class Topic extends Model
{
public static function getTopic($id){
return self::find(['id'=>$id]);
}

public function user(){
return $this->belongsTo('User','user_id');
}
}