如何在mongoose中创建模型模式中的引用

const mongoose = require('mongoose');

// 创建被引用的模型模式
const authorSchema = new mongoose.Schema({
  name: String,
  age: Number
});

// 创建引用的模型模式
const bookSchema = new mongoose.Schema({
  title: String,
  author: {
    type: mongoose.Schema.Types.ObjectId,
    ref: 'Author' // 引用Author模型
  }
});

// 创建模型
const Author = mongoose.model('Author', authorSchema);
const Book = mongoose.model('Book', bookSchema);

Book.find().populate('author').exec((err, books) => {
  if (err) {
    console.error(err);
  } else {
    console.log(books);
  }
});