mongoose and express i want user related data in comment modal

I have a user ,post,comment modal

This is my comment modal

import mongoose from "mongoose";

const CommentSchema = new mongoose.Schema({
  postId: {
    type: mongoose.Schema.Types.ObjectId,
    ref: "Post",
  },
  userId: {
    type: mongoose.Schema.Types.ObjectId,
    ref: "User",
  },
  content: {
    type: String,
    required: true,
  },
  image: {
    type: String,
  },
  likes: {
    type: Array,
    default: [],
  },
});

export default mongoose.model("Comment", CommentSchema);

and this is my addComment controller

export const addComment = async (req, res) => {
  try {
    const post = await Post.findById(req.body.postId);
    if (!post) {
      return res.status(404).json({ message: "Invalid Post Id" });
    }
    const comment = await new Comment(req.body);
    await comment.save();
    res
      .status(200)
      .json({ success: true, message: "Comment added Successfully!" });
  } catch (err) {
    res.status(500).json({ message: "Internal Server Error!" });
  }
};and this is my getComments controller

export const getAllCommentsOfPost = async (req, res) => {
  try {
    const post = await Post.findById(req.body.postId);
    if (!post) {
      return res.status(404).json({ message: "Invalid Post Id" });
    }
    const comments = await Comment.find({ postId: req.body.postId });
    res.status(200).json({ success: true, comments: comments });
  } catch (err) {
    res.status(500).json({ message: "Internal Server Error!" });
  }
};

This is my response

{
    "success": true,
    "comments": [
        {
            "_id": "65f2eec753e8de0aa1fffb26",
            "postId": "65f2e983f80127323fc86d8e",
            "content": "bad",
            "likes": [],
            "__v": 0
        }
    ]
}

in the response i am only getting postId , why am i not getting userId despite mentioning userId in comment modal and referenced it to user Modal and also how can i get the username as well .I need both username and userId in comments modal, can you guys tell me ways to do it?