在mongoose的嵌套查询中按id查找用户

const mongoose = require('mongoose');

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

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

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

const userId = '用户id';

User.findById(userId)
  .populate('posts')
  .exec((err, user) => {
    if (err) {
      console.error(err);
      return;
    }
    console.log(user);
  });