如何将mongo的.native功能化为蓝鸟的承诺？

const Promise = require('bluebird');
const MongoClient = require('mongodb').MongoClient;

// 连接到MongoDB数据库
const url = 'mongodb://localhost:27017/mydb';
const client = MongoClient.connect(url);

// 将collection的find方法转换为蓝鸟的承诺
const collection = client.then(db => db.collection('mycollection'));
const findAsync = Promise.promisifyAll(collection).findAsync;

// 使用蓝鸟的承诺进行查询
findAsync({}).then(docs => {
  console.log(docs);
}).catch(err => {
  console.error(err);
});