$group stage for aggregation in MongoDB - Mini Project: Build & Apply

$group Stage for Aggregation in MongoDB

📖 Scenario: You work at a bookstore that keeps sales records in a MongoDB collection. Each sale document records the bookTitle, author, and copiesSold. You want to find out how many copies of each book were sold in total.

🎯 Goal: Build a MongoDB aggregation pipeline using the $group stage to calculate the total copies sold for each book.

📋 What You'll Learn

Create a collection named sales with documents containing bookTitle, author, and copiesSold fields.

Define a variable pipeline that holds the aggregation stages.

Use the $group stage to group documents by bookTitle and calculate the total copiesSold for each book.

Add a final stage to sort the results by total copies sold in descending order.

💡 Why This Matters

🌍 Real World

Bookstores and many businesses use MongoDB aggregation pipelines to analyze sales data and generate reports.

💼 Career

Understanding the <code>$group</code> stage is essential for data analysts and backend developers working with MongoDB to summarize and aggregate data efficiently.

1

Create the sales data collection

Create a variable called sales that is a list of documents with these exact entries: { bookTitle: "The Hobbit", author: "J.R.R. Tolkien", copiesSold: 5 }, { bookTitle: "1984", author: "George Orwell", copiesSold: 8 }, { bookTitle: "The Hobbit", author: "J.R.R. Tolkien", copiesSold: 3 }, { bookTitle: "Dune", author: "Frank Herbert", copiesSold: 7 }.

MongoDB

# Create the sales data list with exact documents
# Your code here

Need a hint?

Use a list of dictionaries with the exact keys and values as shown.

2

Define the aggregation pipeline variable

Create a variable called pipeline and set it to an empty list to hold the aggregation stages.

MongoDB

sales = [
    { "bookTitle": "The Hobbit", "author": "J.R.R. Tolkien", "copiesSold": 5 },
    { "bookTitle": "1984", "author": "George Orwell", "copiesSold": 8 },
    { "bookTitle": "The Hobbit", "author": "J.R.R. Tolkien", "copiesSold": 3 },
    { "bookTitle": "Dune", "author": "Frank Herbert", "copiesSold": 7 }
]
# Create an empty list called pipeline
# Your code here

Need a hint?

Just create an empty list named pipeline.

3

Add the $group stage to sum copies sold by bookTitle

Add a $group stage to the pipeline list. Group by _id set to $bookTitle and create a field totalCopies that sums copiesSold.

MongoDB

sales = [
    { "bookTitle": "The Hobbit", "author": "J.R.R. Tolkien", "copiesSold": 5 },
    { "bookTitle": "1984", "author": "George Orwell", "copiesSold": 8 },
    { "bookTitle": "The Hobbit", "author": "J.R.R. Tolkien", "copiesSold": 3 },
    { "bookTitle": "Dune", "author": "Frank Herbert", "copiesSold": 7 }
]
pipeline = []
# Add a $group stage to pipeline to group by bookTitle and sum copiesSold
# Your code here

Need a hint?

Use { "$group": { "_id": "$bookTitle", "totalCopies": { "$sum": "$copiesSold" } } } inside the pipeline list.

4

Add a $sort stage to order results by totalCopies descending

Add a $sort stage to the pipeline list that sorts by totalCopies in descending order (-1).

MongoDB

sales = [
    { "bookTitle": "The Hobbit", "author": "J.R.R. Tolkien", "copiesSold": 5 },
    { "bookTitle": "1984", "author": "George Orwell", "copiesSold": 8 },
    { "bookTitle": "The Hobbit", "author": "J.R.R. Tolkien", "copiesSold": 3 },
    { "bookTitle": "Dune", "author": "Frank Herbert", "copiesSold": 7 }
]
pipeline = [
    {
        "$group": {
            "_id": "$bookTitle",
            "totalCopies": { "$sum": "$copiesSold" }
        }
    }
]
# Add a $sort stage to pipeline to sort by totalCopies descending
# Your code here

Need a hint?

Add { "$sort": { "totalCopies": -1 } } as the last stage in the pipeline list.