如何通过使用mongoose查询我的mongodb来获得postIds的长度

const mongoose = require('mongoose');

mongoose.connect('mongodb://localhost:27017/mydatabase', { useNewUrlParser: true, useUnifiedTopology: true });

const postSchema = new mongoose.Schema({
  postIds: [String]
});

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

Post.find({}, (err, posts) => {
  if (err) {
    console.error(err);
  } else {
    const postIdsLength = posts[0].postIds.length;
    console.log('postIds的长度为：', postIdsLength);
  }
});