How to handle mongoDB general operations in node.js

Question

I'm trying to prepare a general function which will allow me to use any function on any database/collection. I'm not sure im doing this correctly. Here's my function code in node.js:

function use_db(db_url, func, ...args) {
    let prom;
    // noinspection JSIgnoredPromiseFromCall
    var lele = MongoClient.connect(db_url, (error, client) => {
        console.log('Connected');
        const db = client.db();

        console.log(db);

        prom = func(db, ...args);
        client.close();
        console.log('Disconnected successfully');
    });
    console.log(lele, 'whaat?');
    return prom;
}

I want it to return value prom but this happens:

first output is console.log(lele, 'whaat?'); which value is undefined 'whaat?'
then 'Connected'
and the last is 'Disconnected successfully'

So obviously prom is not defined at this moment

Why output is in this order? Why console.log(lele, 'whaat?'); runs first? Any ideas how can I improve this function, so it will use any other function to work on specific mognoDB database?

EDIT://

function connectDB(db_url) {
    return new Promise((res, rej) => {
        MongoClient.connect(db_url, (error, client) => {
            if (error) return rej(error);
            console.log('Connected');
            const db = client.db();
            return res({
                db,
                client
            });
        });
    });
}

async function use_db(db_url) {
    console.log('Start');
    const {
        db,
        client
    } = await connectDB(db_url);
    console.log('After db connection');

    return [db, client];
}

let temp_list = use_db(db_url);
const db = temp_list[0];
const client = temp_list[1];

let no_user = can_create_user(db, temp_email);

if(no_user) {
    //some code
}

How Can I leave active connection to the database and use db everytime for other functions? It doesn't wait for promise to resolve

Rahul Sharma · Answer 1 · 2019-04-06T19:08:54.800

0

Node.js is asynchronous it does not wait for any blocker operation. check this

function connectDB(db_url) {
    return new Promise((res, rej) => {
        MongoClient.connect(db_url, (error, client) => {
            if (error) return rej(error);
            console.log('Connected');
            const db = client.db();
            return res({
                db,
                client
            });
        });
    });
}

async function use_db(db_url, func, ...args) {
    console.log('Start');
    try {
        const {
            db,
            client
        } = await connectDB(db_url);
        console.log('After db connection');
        const prom = func(db, ...args);
        client.close();
        console.log('Disconnected successfully');
        return prom;
    } catch (error) {
        console.log(error);
    }
}

edited Apr 06 '19 at 19:08

answered Apr 06 '19 at 19:01

Rahul Sharma

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Thanks for help! I tried it, but it still doesn't seem to be working. I pasted the code above, in the edited question. – SecurityBreach Apr 06 '19 at 20:04
@JavaBoon are you getting any error. – Rahul Sharma Apr 06 '19 at 20:06
`(node:12624) DeprecationWarning: Cursor.each is deprecated. Use Cursor.forEach instead.` and `(node:12624) DeprecationWarning: current URL string parser is deprecated, and will be removed in a future version. To use the new parser, pass option { useNewUrlParser: true } to MongoClient.connect.` Only those two – SecurityBreach Apr 06 '19 at 20:07
1

it's just a warning, not an error. what's `func` function is doing. check this it might help https://stackoverflow.com/questions/55537880/every-second-run-throws-mongoerror-topology-was-destroyed/55538144#55538144 – Rahul Sharma Apr 06 '19 at 20:08
In this case it's a reference to `can_create_user ` – SecurityBreach Apr 06 '19 at 20:11
Alright, I will try it out (the link) – SecurityBreach Apr 06 '19 at 20:12
I checked it out. I learned that the best way is to leave active connection to the database. I attempted to recreate connection everytime i used it. My progress is updated in editet question – SecurityBreach Apr 06 '19 at 20:36

score 0 · Answer 2 · answered Apr 07 '19 at 01:51

Alright, I just worked around this and merged it all in few functions, where each connects to mongo and then disconnects after. I gave up. Here's a working example of adding a user to my database.

function add_user(db_url, name, surname, email, password) {
    MongoClient.connect(db_url, { useNewUrlParser: true }, (error, client) => {
        const db = client.db();

        db.collection('users').find({email: email}).toArray(function(err, result) {
            if(result.length === 0) {
                console.log('Adding new user');
                insert_into_users(db, name, surname, email, sha256(password));
            } else {
                console.log('E-mail already in database');
            }

            client.close();
        });
    });
}

function insert_into_users(db, name, surname, email, password) {
    db.collection('users').insertOne({
        name: name,
        surname: surname,
        email: email,
        password: password,
        liked_films: []
    });
    console.log('New user created');
}

How to handle mongoDB general operations in node.js

2 Answers2