如何使用nodejs创建自引用MongoDB模式和post路由？

npm install express mongoose body-parser

// models/User.js
const mongoose = require('mongoose');
const Schema = mongoose.Schema;

const userSchema = new Schema({
  name: String,
  email: String,
  parent: {
    type: Schema.Types.ObjectId,
    ref: 'User'
  }
});

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

// routes/users.js
const express = require('express');
const router = express.Router();
const User = require('../models/User');

router.post('/', async (req, res) => {
  try {
    const newUser = new User(req.body);
    await newUser.save();
    res.status(201).send(newUser);
  } catch (error) {
    res.status(400).send(error);
  }
});

module.exports = router;

// app.js
const express = require('express');
const mongoose = require('mongoose');
const bodyParser = require('body-parser');
const usersRouter = require('./routes/users');

const app = express();

app.use(bodyParser.json());
app.use('/users', usersRouter);

mongoose.connect('mongodb://localhost:27017/mydatabase', {
  useNewUrlParser: true,
  useUnifiedTopology: true
});

app.listen(3000, () => {
  console.log('Server is running on port 3000');
});

const user = await User.findById(userId).populate('parent');