Connection Events in Mongoose | Rustcode

Connection Events in Mongoose

Mongoose connections emit a variety of events that you can listen for to monitor and react to the state of your MongoDB connection. These events help you track connectivity, errors, reconnection attempts, and more, allowing your application to handle database availability proactively.

Table of Content

Common Connection Events

connecting: Emitted when Mongoose starts making its initial connection to the MongoDB server.
connected: Emitted when Mongoose successfully makes its first connection or reconnects after losing connectivity.
open: Emitted after connected and onOpen is executed on models.
disconnecting: Emitted when Connection#close() is called to disconnect.
disconnected: Emitted when Mongoose loses connection to MongoDB.
reconnected: Emitted when Mongoose successfully reconnects after losing connection.
close: Emitted after the connection has closed successfully.

Setting Up Event Listeners

Listen to events from the mongoose.connection object:

const db = mongoose.connection;

db.on('connecting', () => console.log('Connecting to MongoDB...'));
db.on('connected', () => console.log('Connected to MongoDB!'));
db.on('open', () => console.log('Connection open'));
db.on('disconnecting', () => console.log('Disconnecting from MongoDB'));
db.on('disconnected', () => console.log('Disconnected from MongoDB'));
db.on('reconnected', () => console.log('Reconnected to MongoDB'));
db.on('close', () => console.log('Connection closed'));
db.on('error', err => console.error('Connection error:', err));

Handling Connection Errors

Use the error event to handle and log any errors that occur during the connection lifecycle.

Monitoring Reconnection

Mongoose automatically tries to reconnect when connectivity is lost. Use the reconnected event to confirm when your application regains access to the database.

Example Code

const mongoose = require('mongoose');

mongoose.connect('mongodb://localhost:27017/mydb', { useNewUrlParser: true, useUnifiedTopology: true });

const db = mongoose.connection;

db.on('connecting', () => console.log('Connecting to MongoDB...'));
db.on('connected', () => console.log('Connected to MongoDB!'));
db.on('open', () => console.log('Connection open'));
db.on('disconnecting', () => console.log('Disconnecting from MongoDB'));
db.on('disconnected', () => console.log('Disconnected from MongoDB'));
db.on('reconnected', () => console.log('Reconnected to MongoDB'));
db.on('close', () => console.log('Connection closed'));
db.on('error', err => console.error('Connection error:', err));

Best Practices

Use connection events to provide detailed logging and monitoring.
Implement retry and fallback logic based on connection state.
Gracefully handle disconnections and resource cleanup.
Notify users or administrators on prolonged connectivity issues.

Conclusion

Connection events in Mongoose offer powerful hooks to monitor MongoDB connectivity status and handle events appropriately. Leveraging these events ensures your Node.js applications maintain high availability and resilience against network disruptions.