Fix UnhandledPromiseRejectionWarning: MongooseServerSelectionError

Understanding the MongooseServerSelectionError

When working with Node.js and Mongoose, the MongooseServerSelectionError is indicative of an issue with connecting to a MongoDB database. This connection issue can arise from several factors like incorrect database URI, network issues, or problems with the MongoDB server itself.

Diagnosing the Issue

Begin by verifying the database URI and ensuring that your MongoDB instance is running and accessible. Network configuration such as firewalls, VPNs, or incorrect configuration settings in Mongoose can also contribute to this error.

Applying the Fix

To address the MongooseServerSelectionError, ensure your Mongoose version is up to date. Next, handle promises correctly by using async/await and try/catch blocks for error management. Configure the connection to MongoDB correctly and ensure any network configurations or authentication credentials required are accurate.

Sample Code Example

import mongoose from 'mongoose';

// Async function to connect to the database
const connectDatabase = async () => {
  try {
    await mongoose.connect('mongodb://localhost:27017/mydb', {
      useNewUrlParser: true,
      useUnifiedTopology: true
    });
    console.log('Connected to database successfully');
  } catch (error) {
    // Handle the connection error
    console.error('Database connection failed:', error);
  }
};

// Initialize connection
connectDatabase();

This sample code will attempt to connect to a MongoDB database and log the success message or catch any errors during the connection, including the MongooseServerSelectionError.