How to create sub document in mongoose? MongoDB, NodeJS

Question

I am trying to implement an array of comments as a subdocument, in my main document of posts, I am new to js and mongoose, while I tried updateOne, it is working, but it is not working if I use the save parameter, and if I add another comment, the comment is replacing but not adding as another comment. If I am question is dumb, that is because I am very new, please help me out. image of my document

the codes I tried:

this code works, but as I said, whenever the new comment is made, it is replacing:

//add comment

router.post("/:id/comment", async (req, res) => {
try {
const post = await Post.findById(req.params.id);
const comment = await post.updateOne({ $set: { comments: req.body } });
res.status(200).json(comment);
 } catch (err) {
 res.status(500).json("error");
 }
});

the save parameter:

//add comment

router.post("/:id/comment", async (req, res) => {
try {
const post = await Post.findById(req.params.id);
const comment = await post.save({ $set: { comments: req.body } });
res.status(200).json(comment);
  } catch (err) {
res.status(500).json("error");
 }
});

my model file:

const mongoose = require("mongoose");

const PostSchema = new mongoose.Schema(
{
userId: {
  type: String,
  require: true,
},
description: {
  type: String,
  max: 1000,
},
image: {
  type: Array,
},
likes: {
  type: Array,
  default: [],
},

comments: [
  new mongoose.Schema(
    {
      userId: {
        type: String,
        require: true,
      },
      comment: {
        type: String,
        default: "",
      },
    },
    { timestamps: true }
  ),
],

},

{ timestamps: true }

);

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

Answer 1

You are using wrong update operator. If you want to add an element to an array use $push operator. This will update the array, whereas $set will just set the value you are providing, thus overwriting previous values.