如何在mongoDB post模式中填充post的所有评论？

const mongoose = require('mongoose');

const commentSchema = new mongoose.Schema({
  text: String,
  postId: { 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 Comment = mongoose.model('Comment', commentSchema);
const Post = mongoose.model('Post', postSchema);

Post.aggregate([
  {
    $lookup: {
      from: 'comments', // 评论集合的名称
      localField: 'comments', // Post文档中的字段，存储了评论的ID
      foreignField: '_id', // Comment文档中的字段，与Post文档中的comments字段相对应
      as: 'filledComments' // 将填充后的评论存储在这个字段中
    }
  }
]).exec((err, postsWithComments) => {
  if (err) {
    console.error('Error populating comments:', err);
    return;
  }
  console.log(postsWithComments);
});