如何在Mongoose中统计帖子评论

const Post = require('./models/Post');

Post.aggregate([
  { $match: { _id: postId } }, // 匹配指定的帖子ID
  { $lookup: { from: 'comments', localField: '_id', foreignField: 'postId', as: 'comments' } }, // 关联comments集合，根据postId字段
  { $project: { commentCount: { $size: '$comments' } } } // 计算comments数组的长度，即评论数量
])
.then(result => {
  const commentCount = result[0].commentCount;
  console.log(`帖子评论数量：${commentCount}`);
})
.catch(error => {
  console.error(error);
});