Mongoose | findById() Function

The findById() function is used to find a single document by its _id field. The _id field is cast based on the Schema before sending the command.

Installation of mongoose module:

1. You can visit the link Install mongoose module. You can install this package by using this command.

   npm install mongoose

2. After installing mongoose module, you can check your mongoose version in command prompt using the command.

   npm version mongoose

3. After that, you can just create a folder and add a file for example index.js, To run this file you need to run the following command.

   node index.js

Filename: index.js

const mongoose = require('mongoose');

// Database connection
mongoose.connect('mongodb://127.0.0.1:27017/geeksforgeeks', {
    useNewUrlParser: true,
    useCreateIndex: true,
    useUnifiedTopology: true
});

// User model
const User = mongoose.model('User', {
    name: { type: String },
    age: { type: Number }
});

// Finding a document whose id=5ebadc45a99bde77b2efb20e
var id = '5ebadc45a99bde77b2efb20e';
User.findById(id, function (err, docs) {
    if (err){
        console.log(err);
    }
    else{
        console.log("Result : ", docs);
    }
});

Steps to run the program:

1. The project structure will look like this:
   
2. Make sure you have install mongoose module using following command:

   npm install mongoose

3. Below is the sample data in the database before the function is executed, You can use any GUI tool or terminal to see the database, like we have used Robo3T GUI tool as shown below:
   
4. Run index.js file using below command:

   node index.js

   

So this is how you can use the mongoose findById() function to find a single document by its _id field.

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