FindById Method in Mongoose

The findById() method in Mongoose is one of the most commonly used methods for retrieving a document by its unique identifier (_id) in a MongoDB collection. This article will cover everything we need to know about how to use the findById() method, including syntax, examples, installation, and troubleshooting.

What is the findById() Method in Mongoose?

In Mongoose, findById() is a method used to retrieve a single document by its _id field. This is the primary method to query documents using the unique identifier, typically the _id field, which is automatically generated by MongoDB for each document. This method allows for a simplified querying process, making it easy to retrieve a document based on its _id, ensuring a more efficient and streamlined data retrieval process in our Node.js applications.

Syntax:

Model.findById(id,[projection],[options])

Parameters:

• Model: This is the name of the collection used to retrieve the document corresponding to the provided ID.
• id: This is the identifier for the document you intend to locate.
• projection: projection or query projection specifies the document fields to include or exclude.
• options: specifies additional operations e.g., lean, populate etc.
• callback: findById also accepts a callback function, which can manage errors or perform actions with the retrieved document.

How to Use findById() in Mongoose

The findById() method is very straightforward and can be used to retrieve a document by its _id. Here's how you can use it in your Node.js application.

Example 1: Basic Usage

In this example, we connect to a mongoDB database and retrieves a document by its id with the help of findById() method:

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

Explanation:

• We define a User model with name and age fields.
• We use findById() to retrieve the document by its _id ('5ebadc45a99bde77b2efb20e').
• The document matching the _id is returned and logged in the console.

How to Install Mongoose

Before using findById() or any other Mongoose method, ensure that Mongoose is installed in your Node.js project.

Step 1: Install Mongoose

You can install the Mongoose package in your project directory by running the following command:

npm install mongoose

Step 2: Check Mongoose Version

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

npm version mongoose

Project Structure:

After installation, your package.json file will contain an updated dependencies section like this:

"dependencies": {
    "mongoose": "^7.6.5",
}

Step 3: Run the Application

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

node index.js

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

Common Use Cases for findById()

The findById() method is commonly used in scenarios where you need to fetch a single document by its unique identifier. Some of the typical use cases include:

1. User Authentication: Retrieving user data by their _id after successful login.
2. Document Retrieval in APIs: Fetching individual items from a database based on their unique identifier.
3. Admin Access: Allowing admin users to retrieve or modify a document (e.g., user profiles, blog posts) based on the document’s _id.

Handling Errors and Promises

The findById() method can be used with callbacks or promises. When using Promises, we can handle success and failure scenarios more easily with then() and catch() or async/await.

Example using Promises

User.findById(id)
  .then(user => {
    console.log('User found:', user);
  })
  .catch(err => {
    console.error('Error:', err);
  });

Example using Async/Await

const getUser = async (id) => {
  try {
    const user = await User.findById(id);
    console.log('User found:', user);
  } catch (err) {
    console.error('Error:', err);
  }
};

getUser('5ebadc45a99bde77b2efb20e');

Conclusion

The findById() method in Mongoose is a simple yet powerful function to retrieve a document based on its _id field. It offers a clean and efficient way to query MongoDB by utilizing the unique identifiers that MongoDB automatically generates. With support for Promises and async/await, you can integrate this method into modern JavaScript applications seamlessly. Whether you’re building user authentication systems or fetching items in an API, findById() is an essential tool for handling data retrieval in Mongoose.