如何在mongoose中对嵌套数组使用findById()？

const mongoose = require('mongoose');

const userSchema = new mongoose.Schema({
  posts: [{
    title: String,
    content: String
  }]
});

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

const userId = '用户的ID';
const postId = '要查询的嵌套数组元素的ID';

User.findById(userId, (err, user) => {
  if (err) {
    console.error(err);
    return;
  }

  // 遍历嵌套数组，查找匹配的元素
  const post = user.posts.find(p => p._id.toString() === postId);
  if (post) {
    console.log(post);
  } else {
    console.log('未找到匹配的元素');
  }
});