Read concern levels (local, majority, snapshot) in MongoDB - Mini Project: Build & Apply

Understanding MongoDB Read Concern Levels

📖 Scenario: You are managing a MongoDB database for a small online store. You want to understand how different read concern levels affect the data you read from the database.

🎯 Goal: Learn to set and use different MongoDB read concern levels: local, majority, and snapshot in queries.

📋 What You'll Learn

Create a MongoDB collection with sample documents

Set a read concern level variable

Query the collection using the specified read concern

Complete the query with the correct read concern option

💡 Why This Matters

🌍 Real World

Understanding read concern levels helps ensure your application reads data with the right consistency and freshness, important for financial or inventory systems.

💼 Career

Database administrators and backend developers often configure read concerns to balance performance and data accuracy in distributed databases.

1

Create a collection with sample data

Create a MongoDB collection called products and insert these exact documents: { _id: 1, name: 'Pen', stock: 100 }, { _id: 2, name: 'Notebook', stock: 200 }, and { _id: 3, name: 'Eraser', stock: 150 }.

MongoDB

// Your code here to create 'products' collection and insert documents

Need a hint?

Use insertMany to add multiple documents to the products collection.

2

Set the read concern level

Create a variable called readConcernLevel and set it to the string 'majority'.

MongoDB

db.products.insertMany([
  { _id: 1, name: 'Pen', stock: 100 },
  { _id: 2, name: 'Notebook', stock: 200 },
  { _id: 3, name: 'Eraser', stock: 150 }
])

// Create variable readConcernLevel and set to 'majority'
// Your code here

Need a hint?

Use const to create the variable readConcernLevel and assign the string 'majority'.

3

Query the collection with the read concern

Write a query to find all documents in the products collection using the read concern level stored in readConcernLevel. Use db.products.find() with the readConcern option set to { level: readConcernLevel }.

MongoDB

db.products.insertMany([
  { _id: 1, name: 'Pen', stock: 100 },
  { _id: 2, name: 'Notebook', stock: 200 },
  { _id: 3, name: 'Eraser', stock: 150 }
])

const readConcernLevel = 'majority';

// Query products with readConcern option using readConcernLevel
// Your code here

Need a hint?

Use db.products.find({}, { readConcern: { level: readConcernLevel } }) to query with the read concern.

4

Complete the query to use snapshot read concern

Change the readConcernLevel variable to the string 'snapshot' and update the query to use this new read concern level.

MongoDB

db.products.insertMany([
  { _id: 1, name: 'Pen', stock: 100 },
  { _id: 2, name: 'Notebook', stock: 200 },
  { _id: 3, name: 'Eraser', stock: 150 }
])

// Change readConcernLevel to 'snapshot'
// Update the query to use the new readConcernLevel
// Your code here

Need a hint?

Update the variable readConcernLevel to 'snapshot' and use it in the query options.