Unique index behavior in MongoDB - Mini Project: Build & Apply

Unique Index Behavior in MongoDB

📖 Scenario: You are managing a small online store database using MongoDB. You want to ensure that each product has a unique product code so that no two products can have the same code. This helps avoid confusion when customers order products.

🎯 Goal: Create a MongoDB collection called products with some initial product documents. Then, add a unique index on the product_code field to prevent duplicate product codes. Finally, insert a new product and observe how the unique index enforces uniqueness.

📋 What You'll Learn

Create a products collection with three product documents having product_code and name fields.

Create a unique index on the product_code field in the products collection.

Try to insert a new product with a product_code that already exists and observe the error.

Insert a new product with a unique product_code successfully.

💡 Why This Matters

🌍 Real World

Unique indexes are used in real databases to ensure data integrity, such as preventing duplicate user emails or product codes.

💼 Career

Database administrators and backend developers often create unique indexes to enforce business rules and avoid data duplication.

1

Create the products collection with initial data

Create a MongoDB collection called products and insert these three documents exactly: { product_code: "P001", name: "Notebook" }, { product_code: "P002", name: "Pen" }, and { product_code: "P003", name: "Eraser" }.

MongoDB

// Insert the initial products into the products collection
// Your code here

Need a hint?

Use db.products.insertMany() with an array of product documents.

2

Create a unique index on product_code

Create a unique index on the product_code field in the products collection using db.products.createIndex() with the option { unique: true }.

MongoDB

db.products.insertMany([
  { product_code: "P001", name: "Notebook" },
  { product_code: "P002", name: "Pen" },
  { product_code: "P003", name: "Eraser" }
])
// Create a unique index on product_code
// Your code here

Need a hint?

Use db.products.createIndex({ product_code: 1 }, { unique: true }) to create the unique index.

3

Try inserting a product with a duplicate product_code

Try to insert a new product document { product_code: "P002", name: "Marker" } into the products collection. This should fail because product_code "P002" already exists and the unique index prevents duplicates.

MongoDB

db.products.insertMany([
  { product_code: "P001", name: "Notebook" },
  { product_code: "P002", name: "Pen" },
  { product_code: "P003", name: "Eraser" }
])
db.products.createIndex({ product_code: 1 }, { unique: true })
// Try to insert a product with duplicate product_code "P002"
// Your code here

Need a hint?

Use db.products.insertOne({ product_code: "P002", name: "Marker" }) to try inserting the duplicate.

4

Insert a product with a unique product_code

Insert a new product document { product_code: "P004", name: "Ruler" } into the products collection. This should succeed because product_code "P004" is unique.

MongoDB

db.products.insertMany([
  { product_code: "P001", name: "Notebook" },
  { product_code: "P002", name: "Pen" },
  { product_code: "P003", name: "Eraser" }
])
db.products.createIndex({ product_code: 1 }, { unique: true })
db.products.insertOne({ product_code: "P002", name: "Marker" })
// Insert a product with unique product_code "P004"
// Your code here

Need a hint?

Use db.products.insertOne({ product_code: "P004", name: "Ruler" }) to insert the unique product.