如何在MongoDB中获取嵌套值？

// 连接到MongoDB数据库
const MongoClient = require('mongodb').MongoClient;
const uri = 'mongodb://localhost:27017/mydb';
const client = new MongoClient(uri, { useNewUrlParser: true, useUnifiedTopology: true });

client.connect(err => {
  if (err) throw err;
  
  // 选择要查询的集合
  const collection = client.db("mydb").collection("mycollection");
  
  // 查询条件
  const query = { name: "John" };
  
  // 获取嵌套字段的值
  collection.findOne(query, (err, result) => {
    if (err) throw err;
    
    // 访问嵌套字段
    const city = result.address.city;
    console.log(city);
    
    client.close();
  });
});