$addToSet for unique array additions in MongoDB - Mini Project: Build & Apply

$addToSet for unique array additions

📖 Scenario: You are managing a simple database of users and their favorite fruits. Each user has a list of fruits they like. You want to make sure that when you add a new fruit to a user's list, it only gets added if it is not already there, so the list stays unique.

🎯 Goal: Build a MongoDB update operation using $addToSet to add a fruit to a user's favorite fruits array only if it is not already present.

📋 What You'll Learn

Create a collection called users with one document for a user named John who has favorite fruits ['apple', 'banana'].

Define a variable newFruit with the value 'banana'.

Write an update query using $addToSet to add newFruit to John's favorite fruits array.

Add a final query to find and return John's document after the update.

💡 Why This Matters

🌍 Real World

Managing user preferences or tags in a database where duplicates should be avoided.

💼 Career

Understanding $addToSet is important for database developers and administrators to maintain clean and efficient data.

1

Create the initial user document

Insert a document into the users collection with name set to 'John' and favoriteFruits set to ['apple', 'banana'].

MongoDB

// Insert the user document with name 'John' and favoriteFruits ['apple', 'banana']
// Your code here

Need a hint?

Use db.users.insertOne() to add the document.

2

Define the new fruit to add

Create a variable called newFruit and set it to the string 'banana'.

MongoDB

db.users.insertOne({ name: 'John', favoriteFruits: ['apple', 'banana'] })
// Define newFruit as 'banana'
// Your code here

Need a hint?

Use const newFruit = 'banana' to define the variable.

3

Update the user's favorite fruits using $addToSet

Write an update query using db.users.updateOne() to find the document where name is 'John' and use $addToSet to add newFruit to the favoriteFruits array.

MongoDB

db.users.insertOne({ name: 'John', favoriteFruits: ['apple', 'banana'] })
const newFruit = 'banana';
// Update John's favoriteFruits using $addToSet and newFruit
// Your code here

Need a hint?

Use db.users.updateOne() with a filter and $addToSet to add the fruit uniquely.

4

Retrieve the updated user document

Write a query using db.users.findOne() to find and return the document where name is 'John' after the update.

MongoDB

db.users.insertOne({ name: 'John', favoriteFruits: ['apple', 'banana'] })
const newFruit = 'banana';
db.users.updateOne({ name: 'John' }, { $addToSet: { favoriteFruits: newFruit } });
// Find and return John's document
// Your code here

Need a hint?

Use db.users.findOne() with the filter { name: 'John' } to get the updated document.