Node.js连接MongoDB报MongoExpiredSessionError会话已结束问题问询

• MongoDB Node.js 驱动4.x+版本中，collection.insertOne()为异步方法，返回Promise对象，你的代码未添加await关键字等待操作执行完成，就提前调用client.close()关闭了数据库连接，导致插入操作绑定的会话被提前销毁，触发MongoExpiredSessionError。
• 你的app.js中app.get('/products')未绑定对应的getProducts处理函数，会导致该接口无响应。

1. 修复mongo.js代码 #

给insertOne添加await，同时将client.close()放到finally块中，保证出现异常时数据库连接也能正常关闭：

const MongoClient = require("mongodb").MongoClient;

const url ='xxxxxx'

const createProduct = async (req, res, next) => {
    const newProduct = {
      name: req.body.name,
      price: req.body.price
    };
    const client = new MongoClient(url);
  
    try {
      await client.connect();
      const db = client.db();
      // 新增await等待插入完成
      const result = await db.collection('products').insertOne(newProduct);
    } catch (error) {
      // 可自行添加错误日志打印方便排查
      console.log(error)
      return res.json({message: 'Could not store data.'});
    } finally {
      // 连接关闭逻辑放到finally块，保证异常时也能关连
      client.close();
    }
  
    res.json(newProduct);
  };
  
  const getProducts = async (req, res, next) => {
    const client = new MongoClient(url);
  
    let products;
  
    try {
      await client.connect();
      const db = client.db();
      products = await db.collection('products').find().toArray();
    } catch (error) {
      console.log(error)
      return res.json({message: 'Could not retrieve products.'});
    } finally {
      client.close();
    }
  
    res.json(products);
  };
  
  exports.createProduct = createProduct;
  exports.getProducts = getProducts;

2. 修复app.js代码 #

给get路由绑定处理函数：

const express = require('express');
const bodyParser = require('body-parser')
const mongoPractice =require('./mongo')

const app = express();

app.use(bodyParser.json());

app.post('/products',mongoPractice.createProduct);
// 绑定getProducts处理函数
app.get('/products', mongoPractice.getProducts);

app.listen(3000);

不推荐每次请求都新建MongoClient实例，MongoDB驱动内置了连接池，你可以全局初始化一次MongoClient复用连接，减少频繁建连断连的性能开销，代码示例如下：

// mongo.js 全局初始化连接
const MongoClient = require("mongodb").MongoClient;
const url ='xxxxxx'
// 全局复用client
let client = new MongoClient(url);
let dbInstance = null;

// 初始化连接
const initDb = async () => {
  if (!dbInstance) {
    await client.connect();
    dbInstance = client.db();
  }
  return dbInstance;
}

const createProduct = async (req, res, next) => {
  const newProduct = {
    name: req.body.name,
    price: req.body.price
  };
  try {
    const db = await initDb();
    await db.collection('products').insertOne(newProduct);
  } catch (error) {
    console.log(error)
    return res.json({message: 'Could not store data.'});
  }
  res.json(newProduct);
};

// getProducts方法同理复用initDb获取db实例，不需要每次新建client

内容的提问来源于stack exchange，提问作者Milán Nikolics