TransactWriteItems in DynamoDB - Mini Project: Build & Apply

Using TransactWriteItems in DynamoDB

📖 Scenario: You are managing an online bookstore's inventory and orders using DynamoDB. You want to update the stock quantity of a book and create a new order record at the same time, ensuring both actions succeed or fail together.

🎯 Goal: Build a DynamoDB transaction using TransactWriteItems to update the stock of a book and add a new order atomically.

📋 What You'll Learn

Create a transaction request with exactly two actions: one to update the book stock, one to put a new order item.

Use the TransactWriteItems API structure with Update and Put operations.

Specify the table names Books for the stock update and Orders for the new order.

Use the exact attribute names and values as given for the update and put operations.

💡 Why This Matters

🌍 Real World

In real online stores, updating inventory and creating orders must happen together to avoid selling out-of-stock items.

💼 Career

Understanding DynamoDB transactions is important for backend developers working with AWS to ensure data consistency.

1

Create the initial transaction structure

Create a variable called transaction and assign it a dictionary with a key TransactItems set to an empty list.

DynamoDB

transaction = {
    "TransactItems": []
}
# Your code here

Need a hint?

Start by creating a dictionary named transaction with the key TransactItems as an empty list.

2

Add the update operation for book stock

Add a dictionary to transaction["TransactItems"] representing an Update operation on the Books table. The update should set the attribute Stock to 5 for the item with BookId equal to "B123".

DynamoDB

transaction = {
    "TransactItems": [
        # Add Update operation here
    ]
}
# Your code here

Need a hint?

Add an Update dictionary inside TransactItems with the specified table, key, and update expression.

3

Add the put operation for a new order

Append a dictionary to transaction["TransactItems"] representing a Put operation on the Orders table. The item should have OrderId as "O456", BookId as "B123", and Quantity as 1.

DynamoDB

transaction = {
    "TransactItems": [
        {
            "Update": {
                "TableName": "Books",
                "Key": {"BookId": {"S": "B123"}},
                "UpdateExpression": "SET Stock = :newstock",
                "ExpressionAttributeValues": {":newstock": {"N": "5"}}
            }
        },
        # Add Put operation here
    ]
}
# Your code here

Need a hint?

Append a Put dictionary inside TransactItems with the specified table and item attributes.

4

Complete the transaction request

Ensure the transaction dictionary contains exactly two TransactItems: one Update for the Books table and one Put for the Orders table, with the exact keys and values as specified.

DynamoDB

transaction = {
    "TransactItems": [
        {
            "Update": {
                "TableName": "Books",
                "Key": {"BookId": {"S": "B123"}},
                "UpdateExpression": "SET Stock = :newstock",
                "ExpressionAttributeValues": {":newstock": {"N": "5"}}
            }
        },
        {
            "Put": {
                "TableName": "Orders",
                "Item": {
                    "OrderId": {"S": "O456"},
                    "BookId": {"S": "B123"},
                    "Quantity": {"N": "1"}
                }
            }
        }
    ]
}
# Your code here

Need a hint?

Check that your transaction dictionary has both the update and put operations correctly included.