如何在mongoose中连接两个集合

const mongoose = require('mongoose');

// 定义User集合模型
const userSchema = new mongoose.Schema({
  name: String,
  age: Number,
  posts: [{ type: mongoose.Schema.Types.ObjectId, ref: 'Post' }]
});

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

// 定义Post集合模型
const postSchema = new mongoose.Schema({
  title: String,
  content: String
});

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

// 创建一个User文档，并关联两个Post文档
const user = new User({
  name: 'John',
  age: 25,
  posts: ['post1Id', 'post2Id']
});

// 查询User集合，并填充关联的Post数据
User.findOne({ name: 'John' })
  .populate('posts')
  .exec((err, user) => {
    if (err) {
      console.error(err);
    } else {
      console.log(user);
    }
  });