我想在Node.js中更新表单数据，但每当我运行此代码时，它都会将所有值设置为空

const express = require('express');
const bodyParser = require('body-parser');
const app = express();

// 使用body-parser中间件解析请求体
app.use(bodyParser.urlencoded({ extended: false }));

// 处理POST请求，更新表单数据
app.post('/update', (req, res) => {
  // 获取表单数据
  const formData = req.body;

  // 执行更新操作，这里假设使用了MongoDB数据库
  // 请根据实际情况修改以下代码
  const MongoClient = require('mongodb').MongoClient;
  const url = 'mongodb://localhost:27017';
  const dbName = 'mydb';

  MongoClient.connect(url, (err, client) => {
    if (err) {
      console.error('Failed to connect to database:', err);
      res.status(500).send('Failed to connect to database');
      return;
    }

    const db = client.db(dbName);
    const collection = db.collection('mycollection');

    // 更新数据
    collection.updateOne({ _id: formData.id }, { $set: { field1: formData.field1, field2: formData.field2 } }, (err, result) => {
      if (err) {
        console.error('Failed to update data:', err);
        res.status(500).send('Failed to update data');
        return;
      }

      res.send('Data updated successfully');
    });
  });
});

app.listen(3000, () => {
  console.log('Server is running on port 3000');
});