MongoError: Topology is closed, please connect seems to be related to MongoClient.close() and the client won't work while using it

Question

This question here is closely related but the question and the answer are not very related at all. However, in the comments of that OP's post there is the difficulty of working with .close()... That is where the similarities end.

The issue comes from trying to create an api using the direct nodejs mongodb driver 3.9. I have the client call in the controller because putting it in the server and calling to the client when needed constantly creates a "connect error" so here it is in the controller for full context.

whenever I use .close() in the collection client call it will run once and then every other call after that will cause an error Topology is closed. So, for now I commented it out. I am wondering what is causing this and what might I being doing incorrectly causing this error?

The documentation per the driver states to use this and what the purpose is but it is breaking my api repeatedly.

const express = require('express');
const router = express.Router();

import { MongoClient, MongoCallback, MongoError, MongoNetworkError } from 'node_modules/mongodb';
// const MongoClient = require('node_modules/mongodb').MongoClient;
const dbName = 'HealthCheckup';
const documentName = 'userProfile';
const assert = require('assert');
const url = `mongodb+srv://UserDB:h7srvvvvvvvHFd8@vvvvvvvvvai-cvyrh.azure.mongodb.net/${dbName}?retryWrites=true&w=majority`;
const client = new MongoClient(url, { useNewUrlParser: true, useUnifiedTopology: true});

const findUsers = (client, callback) => {
    // Get the documents collection
    const collection = client.collection(documentName);
    // Insert some documents
    collection.find({}).toArray( (err, result) => {
        // console.log('err **** -------- ', err);
        // console.log('Result -------- ', result);
        callback(err, result);
    });
}

const createUser = (client, callback, req) => {
    // Get the documents collection
    const collection = client.collection(documentName);
    // Insert some documents
    collection.insertOne({
        name: req.body.name,
        firstName: req.body.firstName,
        lastName: req.body.lastName,
        email: req.body.email,
        tokenId: req.body.tokenId,
        userPhoto: req.body.userPhoto
    }, (err, result) => {
        // console.log('err **** -------- ', err);
        // console.log('Result -------- ', result);
        callback(err, result);
    });
}

// localhost:4021/user
router.get('/', (req, res) => {
    client.connect( err => {
        const collection = client.db(dbName);
        if (!err) {
            console.log("Connected successfully to server.");
        } else {
            console.log('Error in DB connection : ', JSON.stringify(err, undefined, 2));
        }
        findUsers(collection, (err, result) => {
            console.log('err 2222222 -------- ', err);
            console.log('Result 2222222 -------- ', result);
            if (!err) { 
                res.send(result); 
            } else {
                console.log('Error retreiving user ', JSON.stringify(err, undefined, 2))
            }
            console.log('BREAKPOINT 00000000000000000');
            // client.close();
        });
    });
});

Answer 1

You are trying to close the client in a request handler, but your client is global.

If you want to have a global client, do not close it in request handlers.

If you want to close the client in request handlers, create the client in the handler of the same request.

Answer 2

There is a bug on MongoDb: reconnection to the client doesn't work. Seems like it will be fixed in version 4.0.0. For now it's beta. If you don't want to use the beta version then don't close the client. Or recreate it in handlers like it was proposed in previous answer.