Connection Error Handling in Mongoose | Rustcode

Connection Error Handling in Mongoose

Handling connection errors effectively is essential for building stable and resilient Node.js applications with Mongoose. This article covers techniques to manage both initial connection errors and errors occurring after the connection has been established, including reconnection and event handling.

Table of Content

Initial Connection Error Handling

When connecting to MongoDB using mongoose.connect(), errors can occur if the server is unreachable or credentials are invalid. Handle these errors using promises with catch() or async/await try/catch blocks.

mongoose.connect('mongodb://localhost/mydb')
  .then(() => console.log('Connected to MongoDB'))
  .catch(err => console.error('Initial connection error:', err));

Listening for Error Events

Mongoose emits error events on the connection after the initial connection for issues such as network errors or malformed messages. Listen for these events to log or react to connection problems:

const db = mongoose.connection;

db.on('error', err => {
  console.error('Mongoose connection error:', err);
});

Handling Reconnection Events

Mongoose attempts automatic reconnection on connection loss and emits events such as disconnected, reconnected, and connected to help you monitor connection state:

db.on('disconnected', () => console.log('Mongoose disconnected'));
db.on('reconnected', () => console.log('Mongoose reconnected'));
db.on('connected', () => console.log('Mongoose connected'));

Server Selection Timeout

If the MongoDB driver cannot find a suitable server after serverSelectionTimeoutMS, it throws a timeout error. You can configure this timeout in your connection options:

mongoose.connect('mongodb://localhost/mydb', {
  serverSelectionTimeoutMS: 5000 // Timeout after 5 seconds
});

Example Code

const mongoose = require('mongoose');

mongoose.connect('mongodb://localhost/mydb', {
  useNewUrlParser: true,
  useUnifiedTopology: true,
  serverSelectionTimeoutMS: 5000
})
  .then(() => console.log('Connected to MongoDB'))
  .catch(err => console.error('Connection error:', err));

const db = mongoose.connection;

db.on('error', err => console.error('Connection error event:', err));
db.on('disconnected', () => console.log('Disconnected from MongoDB'));
db.on('reconnected', () => console.log('Reconnected to MongoDB'));

Best Practices

Always catch connection promise rejections to handle initial errors.
Listen for connection events to monitor state changes and errors.
Configure serverSelectionTimeoutMS according to your application needs.
Implement retry logic or alerts on repeated disconnections.
Gracefully close connections on application shutdown.

Conclusion

Robust connection error handling in Mongoose is vital to ensure your application can gracefully handle database connectivity issues. By combining promise rejection handling, event listening, and proper configuration, you can build resilient Node.js applications that maintain stable connectivity with MongoDB servers.