Mongoose Schema API Connection.prototype.readyState

The Connection.prototype.readyState property of the Mongoose API is used on the Connection object. It allows us to determine the state of the connection object. Using this method we can identify in which of the following state disconnected, connecting, connected, and disconnecting connection object is currently present. Let us understand readyState property using an example.

The following list represent different connection ready states:

• 0: disconnected
• 1: connecting 
• 2: connected 
• 3: disconnecting

Syntax:

connection.readyState;

Parameters: This is a property and does not accepts any parameter.

Return Value: This method returns numeric number based on event name which represents the current state of the connection object.

Setting up Node.js Mongoose Module:

Step 1: Create a Node.js application using the following command:

npm init

Step 2: After creating the NodeJS application, Install the required module using the following command:

npm install mongoose

Project Structure: The project structure will look like this: 

Example 1: The below example illustrates the basic functionality of the Mongoose Connection readyState property. We are able to track connection object current state using this property.

Filename: app.js

Javascript

// Require mongoose module
const mongoose = require("mongoose");

// Set Up the Database connection
const URI = "mongodb://localhost:27017/geeksforgeeks"

const connectionObject = mongoose.createConnection(URI, {
    useNewUrlParser: true,
    useUnifiedTopology: true,
});

connectionObject.on('connected', () => {
    console.log('Connected', connectionObject.readyState);
});

Step to run the program: To run the application execute the below command from the root directory of the project:

node app.js

Output:

Connected 1

Example 2: The below example illustrates the basic functionality of the Mongoose Connection readyState property. We are able to track connection object current state using this property. At the end, we are calling close() method in connected event in order to close the connection, and we can see connection object in disconnecting and disconnected state.

Filename: app.js

Javascript

// Require mongoose module
const mongoose = require("mongoose");

// Set Up the Database connection
const URI = "mongodb://localhost:27017/geeksforgeeks"

const connectionObject = mongoose.createConnection(URI, {
    useNewUrlParser: true,
    useUnifiedTopology: true,
});

connectionObject.on('connected', () => {
    console.log('Connected', connectionObject.readyState);
    connectionObject.close()
});

connectionObject.on('disconnecting', () => {
    console.log('Disconnecting ', connectionObject.readyState);
});

connectionObject.on('disconnected', () => {
    console.log('Disconnected ', connectionObject.readyState);
});

Step to run the program: To run the application execute the below command from the root directory of the project:

node app.js

Output:

Connected 1
Disconnecting  3
Disconnected  0

Reference: https://mongoosejs.com/docs/api/connection.html#connection_Connection-readyState