如何在Node.js/Express中间件中正确使用MongoDB Atlas连接？

环境 #

• Node.js (18 LTS) / Express (^4.18.2)
• MongoDB Native Driver (^4.12.0)
• MongoDB Atlas (5.0.14)

项目结构 #

.github  
config  
 - mongodb_client.js  
dist  
middleware  
node_modules  
routes  
src
views
.env  
.gitignore
app.js  
package.json  
README.md  

官方连接代码 #

MongoDB Atlas提供的标准连接代码如下：

const { MongoClient, ServerApiVersion } = require('mongodb');

const uri = "mongodb+srv://admin:<password>@cluster0.******.mongodb.net/?retryWrites=true&w=majority";

const client = new MongoClient(uri, { useNewUrlParser: true, useUnifiedTopology: true, serverApi: ServerApiVersion.v1 });

client.connect(err => {
  const collection = client.db("test").collection("devices");
  // 在此执行集合操作
  client.close();
});

需求目标 #

官方代码在单个文件内完成连接和数据库调用，但我需要实现：

• 单独创建一个存储MongoDB Atlas连接的文件（如mongodb_client.js）
• 将连接实例导出，供中间件文件（如my_middleware_01.js）复用

伪代码示例：

config/mongodb_client.js #

import { MongoClient, ServerApiVersion } from 'mongodb'; 

const connection_string = process.env.MONGODB_CONNECTION_STRING;

const mongodb_client = new MongoClient(connection_string, { useNewUrlParser: true, useUnifiedTopology: true, serverApi: ServerApiVersion.v1 });

// 导出连接实例
export { mongodb_client };

middleware/my_middleware_01.js #

import { mongodb_client } from '../config/mongodb_client.js';

const api_myResource_get = async (req, res) => {
    mongodb_client.open();
    let collection = mongodb_client.db('myDatabase').collection('myCollection');
    let result = await collection.findOne(query, options);  
    res.json({ result: result });
    mongodb_client.close();  
}; 

export { api_myResource_get };

已尝试方案 #

一年前我曾解决过类似问题，但当前MongoDB驱动规范已更新：

• 当前实例化客户端方式：

const client = new MongoClient(connection_string, { useNewUrlParser: true, useUnifiedTopology: true, serverApi: ServerApiVersion.v1 });

• 旧版本方式：

await MongoClient.connect(connection_string);

我搜索了相关问题，但结果多基于旧规范，希望采用最新最佳实践。

尝试1：类封装连接（报错） #

该方案返回错误：TypeError: Cannot read properties of null (reading 'db')

config/mongodb_connection.js

import { MongoClient, ServerApiVersion } from 'mongodb'; 

const connection_string = process.env.MONGODB_CONNECTION_STRING;

class mongodb_connection {
  static async open() {
    if (this.conn) return this.conn;
    this.conn = await MongoClient.connect(connection_string, { useNewUrlParser: true, useUnifiedTopology: true, serverApi: ServerApiVersion.v1 });
    return this.conn;
  }
}

mongodb_connection.conn = null;
mongodb_connection.url = connection_string;

export { mongodb_connection };

middleware/api_mongodb_get.js

import { mongodb_connection } from '../../config/mongodb_connection.js';

const api_mongodb_get = async (req, res) => {

    try {
        mongodb_connection.open();
        const collection = mongodb_connection.conn.db('pages').collection('pages');
        const result = await collection.findOne({ "my_key": "my value" }); 

        res.json({ data: result });
        mongodb_connection.close();
    } catch (error) {
        console.error(error);
        res.status(500).send(error);
    }

};

export { api_mongodb_get };

尝试2：直接导出客户端实例（可运行，但存疑） #

该方案能正常运行，但不确定是否为最佳实践，是否存在潜在问题。

config/mongodb_connection.js

import { MongoClient, ServerApiVersion } from 'mongodb'; 

const connection_string = process.env.MONGODB_CONNECTION_STRING;

const mongodb_connection = new MongoClient(connection_string, { useNewUrlParser: true, useUnifiedTopology: true, serverApi: ServerApiVersion.v1 });

export { mongodb_connection };

middleware/api_mongodb_get.js

import { mongodb_connection } from '../../config/mongodb_connection.js';

const api_mongodb_get = async (req, res) => {

    try {
            mongodb_connection.connect(async err => {  

                const collection = mongodb_connection.db('pages').collection('pages');
                const result = await collection.findOne({ "my_key": "my value" }); 

                res.json({ data: result });
                
                mongodb_connection.close();
            });
    } catch (error) {
        console.error(error);
        res.status(500).send(error);
    }

};

export { api_mongodb_get };

内容的提问来源于stack exchange，提问作者user1063287