Mongoose填充多个级别

const mongoose = require('mongoose');

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

const postSchema = new mongoose.Schema({
  title: String,
  content: String,
  comments: [{
    type: mongoose.Schema.Types.ObjectId,
    ref: 'Comment'
  }]
});

const commentSchema = new mongoose.Schema({
  text: String,
  author: {
    type: mongoose.Schema.Types.ObjectId,
    ref: 'User'
  }
});

// 定义模型
const User = mongoose.model('User', userSchema);
const Post = mongoose.model('Post', postSchema);
const Comment = mongoose.model('Comment', commentSchema);

// 查询用户及其帖子和评论
User.findOne({ name: 'John' })
  .populate({
    path: 'posts',
    populate: {
      path: 'comments',
      populate: {
        path: 'author'
      }
    }
  })
  .exec((err, user) => {
    if (err) {
      console.error(err);
    } else {
      console.log(user);
    }
  });