Mongoose Query.prototype.distinct() API

The Mongoose Query API distinct() method is used to find the distinct values for a particular field in a collection and return the response as an array.

Syntax:

Query.prototype.distinct(field, filter, callback)

Parameters: It accepted the following parameters as mentioned above and described below:

• field: It is a string that identifies the field for which to return the distinct values.
• filter: It is an optional mongoose object which is derived from Query.prototype.setOptions().
• callback: It is a callback function that accepts 2 parameters: error and arr.

Return type: It returns a Query object as a response.

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
touch main.js

Step 2: After completing the Node.js application, Install the required module using the following command:

npm install mongoose

Example 1: In this example, we will use this method to find the distinct values for the field “age” in the collection.

Filename: main.js

Javascript

// Importing the module
const mongoose = require('mongoose')

// Connecting to the database
mongoose.connect('mongodb://localhost:27017/query-helpers',
    {
        dbName: 'event_db',
        useNewUrlParser: true,
        useUnifiedTopology: true
    }, err => err ? console.log(err)
        : console.log('Connected to database'));

const personSchema = new mongoose.Schema({
    name: {
        type: String,
    },
    age: {
        type: Number,
    }
});

const personsArray = [
    {
        name: 'Luffy',
        age: 20
    },
    {
        name: 'Nami',
        age: 20,
    },
    {
        name: 'Zoro',
        age: 35
    }
]

const Person = mongoose.model('Person', personSchema);

(async () => {
    await Person.insertMany(personsArray);
    const res = await Person.distinct('age');
    console.log({ res });
})()

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

node main.js

Output: 

GUI Representation of the  Database using MongoDB Compass:

Example 2: In this example, we will use this method to find the distinct values for the field “name” in the collection.

Filename: main.js

Javascript

// Importing the module
const mongoose = require('mongoose')

// Connecting to the mongodb
mongoose.connect('mongodb://localhost:27017/query-helpers',
    {
        dbName: 'event_db',
        useNewUrlParser: true,
        useUnifiedTopology: true
    }, err => err ? console.log(err)
        : console.log('Connected to database'));

const personSchema = new mongoose.Schema({
    name: {
        type: String,
    },
    age: {
        type: Number,
    }
});

const personsArray = [
    {
        name: 'Luffy',
        age: 20
    },
    {
        name: 'Nami',
        age: 20,
    },
    {
        name: 'Zoro',
        age: 35
    }
]

const Person = mongoose.model('Person', personSchema);

(async () => {
    await Person.insertMany(personsArray);
    const res = await Person.distinct('name');
    console.log({ res });
})()

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

node main.js

Output: 

GUI Representation of the  Database using MongoDB Compass:

Reference: https://mongoosejs.com/docs/api/query.html#query_Query-distinct