I have mongodb setup locally and I created a database with a collection couples. I verified this using mongosh:

This is the code that connects to the database:

databaseConfig.ts

import { MongoClient } from 'mongodb';

const uri = process.env.MONGODB_URI || 'mongodb://127.0.0.1:27017/memory-box';

export const client = new MongoClient(uri);

export async function connectToDatabase() {
    try {
        await client.connect();
        console.log('Connected to the database');
    } catch (error) {
        console.error('Error connecting to the database:', error);
    }
}

This is how I use it:

server.ts

async function startServer() {
  try {
    await connectToDatabase(); // Connect to the database
    app.listen(PORT, () => {
      console.log(`Server is running on port ${PORT}`);
    });
  } catch (error) {
    console.error('Failed to start the server:', error);
  }
}

startServer();

This is the function that creates a couple:

coupleService.ts

export async function createCouple(name1: string, email1: string, name2: string, email2: string): Promise<CoupleType> {
    try {
        const newCouple = new Couple({
            name1,
            email1,
            name2,
            email2,
        });

        const savedCouple = await newCouple.save();
        return savedCouple;
    } catch (error) {
        throw new Error(`Failed to create couple: ${error.message}`);
    }
}

This is the couple model:

Couple.ts

import mongoose, { Model } from 'mongoose';
import coupleSchema from '../schemas/coupleSchema';
import { CoupleType } from '../types/coupleTypes';

const Couple: Model<CoupleType> = mongoose.model<CoupleType>('Couple', coupleSchema);

export default Couple;

This is the couple schema:

coupleSchema.ts

import { Schema } from 'mongoose';

const coupleSchema = new Schema(
    {
        name1: {
            type: String,
            required: true,
        },
        email1: {
            type: String,
            required: true,
            match: [/^S+@S+.S+$/, 'Please use a valid email address.'],
        },
        name2: {
            type: String,
            required: true,
        },
        email2: {
            type: String,
            required: true,
            match: [/^S+@S+.S+$/, 'Please use a valid email address.'],
        },
    },
    {
        timestamps: true, 
    }
);

export default coupleSchema;

When I use postman to create a couple it logs this:

Connected to the database
Server is running on port 3000
???? ~ createCoupleHandler ~ req.body: {
  name1: 'John Doe',
  email1: '[email protected]',
  name2: 'Jane Doe',
  email2: '[email protected]'
}
???? ~ createCoupleHandler ~ error: Error: Failed to create couple: Operation `couples.insertOne()` buffering timed out after 10000ms

I’m not sure what’s going on. It seems to be connecting to the database properly but unable to create the couple.

I tried to access the couple collection manually and insert the document and it works:

export async function connectToDatabase() {
    try {
        // Connect to the MongoDB server
        await client.connect();
        console.log('Connected to the database');

        /** DEBUGGING THE BUFFER ISSUE */
        // List all collections in the connected database
        const database = client.db();

        const couplesCollection = database.collection('couples');

        // Insert a couple into the couples collection
        const result = await couplesCollection.insertOne({
            name1: 'John Doe',
            email1: '[email protected]',
            name2: 'Jane Doe',
            email2: '[email protected]',
        });
        console.log('Inserted couple:', result.insertedId);

        // Find all couples in the couples collection and log them
        const allCouples = await couplesCollection.find().toArray();
        console.log('All couples:', allCouples);

        const collections = await database.listCollections().toArray();
        console.log('Collections:', collections.map(collection => collection.name));
    } catch (error) {
        console.error('Error connecting to the database:', error);
    }
}

So I think the Couple model in the service isn’t accessing the database instance or something like that.
Any idea what’s going on?