Mongoose Query.prototype.findOne() API

Last Updated : 27 Mar, 2023

The Mongoose Query API findOne() method is used to find a single document, from a collection, using the MongoDB query system.

Syntax:

Query.prototype.findOne(filter, projection, options)

Parameters: It accepts the following 4 parameters as mentioned above and described below:

filter: It is a mongoose object which identifies the existing document to replace.
projection: It is a mongoose object that determines the optional fields to return.
options: It is an optional mongoose object which is derived from Query.prototype.setOptions().

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 an existing document that has the name “Luffy”.

Javascript

const mongoose = require('mongoose')
 
// Database connection
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: 19
    },
    {
        name: 'Nami',
        age: 20,
    },
    {
        name: 'Zoro',
        age: 35
    }
]
 
const Person = mongoose.model('Person', personSchema);
 
(async () => {
    await Person.insertMany(personsArray);
    const res = await Person.findOne({ name: "Luffy" });
    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 a single document that has an age equal to “19”.

Javascript

const mongoose = require('mongoose')
 
// Database connection
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: 19
    },
    {
        name: 'Nami',
        age: 20,
    },
    {
        name: 'Zoro',
        age: 35
    }
]
 
const Person = mongoose.model('Person', personSchema);
 
(async () => {
    await Person.insertMany(personsArray);
    const res = await Person.findOne({ age: 19 });
    console.log({ res });
})()