Laravel Eloquent update 的时候如何返回受影响的行数?

$num = $comment->where('create_user_id', auth()->user()->id)->update(['is_delete' => Comment::DELETED]);
这个$num不是受影响行数, 我很需要这个影响行数, 怎么去获取通过Eloquent方法

 public function del(Comment $comment)
    {
        if (auth()->user()->id != $comment->create_user_id) {
            throw new APIException('只允许删除自己发布的评论');
        }

        if ($comment->is_delete == Comment::DELETED) {
            throw new APIException('该评论已经被删除');
        }

        $comment->where('create_user_id', auth()->user()->id)
            ->update(['is_delete' => Comment::DELETED]);

        $comment->article()->decrement('total_comment');

        return responseSuccess('删除评论成功');
    }