如何将mongoose聚合结果转换为特定的文档模式类型？

const mongoose = require('mongoose');

// 定义模式
const authorSchema = new mongoose.Schema({
  name: String,
  books: [{ type: mongoose.Schema.Types.ObjectId, ref: 'Book' }]
});

const bookSchema = new mongoose.Schema({
  title: String,
  author: { type: mongoose.Schema.Types.ObjectId, ref: 'Author' }
});

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

// 聚合查询
Author.aggregate([
  {
    $lookup: {
      from: 'books',
      localField: 'books',
      foreignField: '_id',
      as: 'books'
    }
  }
])
.then(authors => {
  // 将聚合结果中的引用字段替换为文档对象
  return Author.populate(authors, { path: 'books' });
})
.then(populatedAuthors => {
  console.log(populatedAuthors);
})
.catch(error => {
  console.error(error);
});