// backendmodelsPlaylist.js
const mongoose = require('mongoose');

const playlistSchema = new mongoose.Schema({
    name: { type: String, required: true },
    videos: [{ type: mongoose.Schema.Types.ObjectId, ref: 'Video' }],
    userId: { type: mongoose.Schema.Types.ObjectId, ref: 'User' },
});

module.exports = mongoose.model('Playlist', playlistSchema);

// backendmodelsVideo.js
const mongoose = require('mongoose');

const commentSchema = new mongoose.Schema({
  userId: { type: mongoose.Schema.Types.ObjectId, ref: 'User' },
  username: { type: String, required: true },
  comment: { type: String, required: true },
  date: { type: Date, default: Date.now },
});

const videoSchema = new mongoose.Schema({
  title: String,
  description: String,
  url: String,
  uploadDate: {
    type: Date,
    default: Date.now,
  },
  uploader: { type: mongoose.Schema.Types.ObjectId, ref: 'User' },
  likes: [{ type: mongoose.Schema.Types.ObjectId, ref: 'User' }],
  comments: [commentSchema],
  cloudinary_id: { type: String, required: true },
});

module.exports = mongoose.model('Video', videoSchema);

// backendmodelsUser.js
const mongoose = require('mongoose');

const bcrypt = require('bcrypt');

const userSchema = new mongoose.Schema({
  username: { type: String, required: true, unique: true },
  password: { type: String, required: true },
});

userSchema.pre('save', async function (next) {
  if (this.isModified('password')) {
    this.password = await bcrypt.hash(this.password, 10);
  }
  next();
});

userSchema.methods.comparePassword = function (password) {
  return bcrypt.compare(password, this.password);
};

module.exports = mongoose.model('User', userSchema);

The Playlist Modal has reference to Video Modal, The Video Modal has reference to User Modal, but I am receiving only the id’s present in the Video Model not Video Modal itself. Explain in a simple & intuitive way. I am looking for a clear & easy to understand explanation.

This is how I am accessing using API

router.get('/playlist/:id/videos', authMiddleware, async (req, res) => {
    try {
        const playlist = await Playlist.findById(req.params.id)
            .populate({
                path: 'videos',
                populate: { path: 'uploader' }
            });
        if (playlist.userId.toString() !== req.userData.userId) {
            return res.status(403).json({ message: 'Forbidden' });
        }
        res.json(playlist.videos);
    } catch (err) {
        res.status(500).json({ message: err.message });
    }
});

I made necessary changes to the code by adding populate() method, but getting the same issue.