如何在mongoose中通过查询引用对象获取数据

const mongoose = require('mongoose');

// 定义User模式和模型
const userSchema = new mongoose.Schema({
  name: String,
  age: Number,
});

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

// 定义Post模式和模型，引用了User模式
const postSchema = new mongoose.Schema({
  title: String,
  content: String,
  author: {
    type: mongoose.Schema.Types.ObjectId,
    ref: 'User',
  },
});

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

const user = new User({
  name: 'John',
  age: 25,
});

const post = new Post({
  title: 'Introduction to Mongoose',
  content: 'Mongoose is an Object Data Modeling (ODM) library for MongoDB.',
  author: user._id,
});

Post.findOne({ title: 'Introduction to Mongoose' })
  .populate('author')
  .exec((err, post) => {
    if (err) {
      console.error(err);
    } else {
      console.log(post);
      // 输出结果：
      // {
      //   title: 'Introduction to Mongoose',
      //   content: 'Mongoose is an Object Data Modeling (ODM) library for MongoDB.',
      //   author: {
      //     _id: '60f8e8a7a8c5e60015a7f2e1',
      //     name: 'John',
      //     age: 25,
      //   }
      // }
    }
  });