在MongoDB中填充不返回引用

Question

我有两个模式，

// Post.js
const mongoose = require("mongoose");
const Schema = mongoose.Schema;

const postSchema = new Schema({
  user: {
    type: mongoose.Schema.Types.ObjectId,
    ref: "user"
  },
  likes: [
    {
      type: mongoose.Schema.Types.ObjectId,
      ref: "postLike"
    }
  ],
  date: {
    type: Date,
    default: Date.now
  }
});

module.exports = Post = mongoose.model("post", postSchema);

和

//PostLike.js
const mongoose = require("mongoose");
const Schema = mongoose.Schema;

const postLikeSchema = new Schema({
  post: {
    type: mongoose.Schema.Types.ObjectId,
    ref: "post"
  },
  user: {
    type: mongoose.Schema.Types.ObjectId,
    ref: "user"
  },
  // Flag to denote like or dislike
  likeOrDislike: {
    type: Boolean,
    required: true
  },
  date: {
    type: Date,
    default: Date.now
  }
});

module.exports = PostLike = mongoose.model("postLike", postLikeSchema);

我对帖子进行投票时，它会像这样将其保存在PostLike中：

但是当我尝试检索帖子时

let post = await Post.find({ _id: id }).populate("likes");

console.log(post);

return res.json(post);

它返回长度为0的点赞数组，

 [ likes: [],
 date: 2019-09-03T07:03:02.481Z,
 user: 5d495163bd47260574dff2c4,
 __v: 0 } ]

不确定从这里要去哪里。我尝试用.populate("postLike");填充，但这也不起作用。在保存喜欢或不喜欢的方法中，我还必须执行Post.findOneAndUpdate(...)吗？因为这样做消除了在架构中包含引用的全部问题。