Javascript 如何在nodejs中计算mongdb模式中的数组对象？

我想计算一下喜欢和评论的数量，它们都是架构中的数组。架构如下所示：

const PostSchema = new mongoose.Schema({
  text: {
    type: String,
    required: "Name is required",
  },

  photo: {
    data: Buffer,
    contentType: String,
  },
  likes: [{ type: mongoose.Schema.ObjectId, ref: "User" }],
  comments: [
    {
      text: String,
      created: { type: Date, default: Date.now },
      postedBy: { type: mongoose.Schema.ObjectId, ref: "User" },
      likes: Number,
    },
  ],
  postedBy: { type: mongoose.Schema.ObjectId, ref: "User" },
  created: {
    type: Date,
    default: Date.now,
  },
});

由于like和comments都是数组，我想计算它们内部的元素数量，我就是这样做的，我读过关于聚合函数的文章，但不知道如何在这里使用它，因为我必须遍历所有的post文档并获取它们的like和comments

const leaderboard = (req, res) => {
  Post.find({}, function (err, docs) {
    docs.forEach(function (data) {
      var userid = data.postedBy;
      console.log(userid);
      var likes = data.likes.length;
      console.log(likes);
      var comments = data.comments.length;
      console.log(comments);
      const date2 = new Date();
      const diffTime = Math.abs(date2 - data.created);
      const diffDays = Math.ceil(diffTime / (1000 * 60 * 60 * 24));
      console.log(diffDays);
      const updated = User.findByIdAndUpdate(
        userid,
        {score: likes+comments+diffDays },
        function (errr, doc) {
          if (errr) {
            console.log(err);
          } else {
            console.log("Updated User : ", doc);
          }
        }
      );

我会非常感谢你的帮助，谢谢

您可以尝试计数

注释
和
喜欢的元素数

Post.aggregate([
    {$project: {_id: 1, count: {$commentssize: '$comments'},count: {$sizelikes: '$likes'}}
])