mongoose如何自动生成另一组Id？

const mongoose = require('mongoose');
const Schema = mongoose.Schema;
const autopopulate = require('mongoose-autopopulate');

const userSchema = new Schema({
  name: String,
  posts: [
    {
      type: Schema.Types.ObjectId,
      ref: 'Post',
      autopopulate: true, // 开启自动填充
    },
  ],
});

userSchema.plugin(autopopulate);

const postSchema = new Schema({
  title: String,
});

const User = mongoose.model('User', userSchema);
const Post = mongoose.model('Post', postSchema);

// 创建用户和帖子
const user = new User({
  name: 'John',
  posts: [],
});

const post = new Post({
  title: 'Hello World',
});

// 自动填充帖子数据
user.posts.push(post);

// 保存用户和帖子到数据库
user.save((err, savedUser) => {
  // 处理错误和保存成功后的逻辑
});

const mongoose = require('mongoose');
const Schema = mongoose.Schema;

const userSchema = new Schema({
  name: String,
  posts: [
    {
      type: Schema.Types.ObjectId,
      ref: 'Post',
    },
  ],
});

const postSchema = new Schema({
  title: String,
});

const User = mongoose.model('User', userSchema);
const Post = mongoose.model('Post', postSchema);

// 创建用户和帖子
const user = new User({
  name: 'John',
  posts: [],
});

const post = new Post({
  title: 'Hello World',
});

// 手动填充帖子数据
user.posts.push(post._id);

// 保存用户和帖子到数据库
user.save((err, savedUser) => {
  // 处理错误和保存成功后的逻辑
});