Mongoose Schemas Indexes

Mongoose is a MongoDB object modeling and handling for a node.js environment. When a document is produced, Mongoose automatically uses the _id property to index all of the models. We can use Mongoose to define the path-level indexes in our schema. For each defined index in the schema, Mongoose automatically runs createIndex when the application first launches.

Creating node application and Installing Mongoose:

Step 1: Create a node application using the following command:

mkdir folder_name
cd folder_name
npm init -y

Step 2: Install the required module using the following command:

npm install mongoose

Project Structure: It will look like the following.

Example 1: In this example, we will create some documents and see the default indexes, which is set by the mongoose automatically.

Javascript

// Require the mongoose module
const mongoose = require('mongoose');

// Path to our Database
const url = 'mongodb://localhost:27017/GFG'

// Connecting to database
mongoose.connect(url)
    .then((ans) => {
        console.log("Connected  successfully")
    })
    .catch((err) => {
        console.log("Error in the Connection")
    })

// Calling Schema class
const Schema = mongoose.Schema;

// Creating Structure of the collection
const collection_structure = new Schema({
    name: String,
    marks: Number,
})

// Creating collection
const collections = mongoose.model("GFG", collection_structure)

collections.create({
    name: `Ragavpp`,
    marks: 13,
})
    .then((ans) => {
        console.log("Document inserted")
    })

    .catch((err) => {
        console.log(err.Message);
    })

Step to Run Application: Run the application using the following command from the root directory of the project:

node script.js

Output:

Connected Successful
Document inserted

Following we can see the default indexes in Atlas GUI: 

indexes output

Example 2:  In this example, we will create indexes with mobile_No. 

Javascript

// Require the mongoose module
const mongoose = require('mongoose');

// Path to our cloud DataBase
const url = 'mongodb://localhost:27017/GFG'

// Connecting to database
mongoose.set('strictQuery', false);

mongoose.connect(url)
    .then((ans) => {
        console.log("Connected Successful")
    })
    .catch((err) => {
        console.log("Error in the Connection")
    })

// Calling Schema class
const Schema = mongoose.Schema;

// Creating Structure of the collection
// And making indexes using mobile
const collection_structure = new Schema({
    name: {
        type: String,
        require: true,
    },
    marks: {
        type: Number,
        default: 0
    },
    mobile: {
        type: Number,
        index: true,
        require: true,
    }
})

// Creating collection
const collections = mongoose.model("GFG", collection_structure)

collections.create({
    name: `Sam Snehil`,
    marks: 88,
    mobile: 9338948473,
})
    .then((ans) => {
        console.log("Document inserted")
    })

    .catch((err) => {
        console.log(err);
    })

Step to Run Application: Run the application using the following command from the root directory of the project:

node script2.js

Step to Run Application: Run the application using the following command from the root directory of the project:

node main.js

Output:

Following we can see the mobile in indexes on Atlas GUI:

index output2

Reference: https://mongoosejs.com/docs/guide.html#indexes