Transaction conditions in DynamoDB - Mini Project: Build & Apply

DynamoDB Transaction Conditions

📖 Scenario: You are managing a simple inventory system for a small store. You want to update the stock quantity of a product only if the current stock matches a specific value, to avoid overwriting changes made by others.

🎯 Goal: Build a DynamoDB transaction that updates the stock quantity of a product only if the current stock quantity matches the expected value, using transaction conditions.

📋 What You'll Learn

Create a DynamoDB table named Products with ProductID as the primary key.

Set up an initial item with ProductID 'P1001' and Stock 50.

Define a transaction condition to check that the current Stock is 50 before updating.

Update the Stock to 45 only if the condition is met.

💡 Why This Matters

🌍 Real World

Inventory management systems often require safe updates to stock levels to prevent conflicts when multiple users or systems update the same data.

💼 Career

Understanding DynamoDB transactions and condition expressions is essential for backend developers working with AWS to ensure data consistency and integrity.

1

Create the initial item in the Products table

Write a DynamoDB PutItem request to add an item to the Products table with ProductID set to 'P1001' and Stock set to 50.

DynamoDB

# Your PutItem request here

Need a hint?

Use PutItem with TableName 'Products' and set ProductID and Stock attributes.

2

Define the transaction condition for stock check

Create a condition expression variable named conditionExpression that checks if the Stock attribute equals 50.

DynamoDB

PutItem {
  TableName: "Products",
  Item: {
    "ProductID": { S: "P1001" },
    "Stock": { N: "50" }
  }
}

# Define conditionExpression to check Stock equals 50

Need a hint?

Use a condition expression string and an expression attribute value for 50.

3

Create the transaction update with condition

Write a DynamoDB TransactWriteItems request that updates the Stock attribute to 45 for ProductID 'P1001' only if the conditionExpression is true.

DynamoDB

PutItem {
  TableName: "Products",
  Item: {
    "ProductID": { S: "P1001" },
    "Stock": { N: "50" }
  }
}

conditionExpression = "Stock = :expectedStock"
ExpressionAttributeValues = { ":expectedStock": { N: "50" } }

# Write TransactWriteItems request with Update and ConditionExpression

Need a hint?

Use TransactWriteItems with an Update action including ConditionExpression and UpdateExpression.

4

Complete the transaction with final attributes

Add the final ExpressionAttributeValues to the transaction update to include both :newStock as 45 and :expectedStock as 50.

DynamoDB

PutItem {
  TableName: "Products",
  Item: {
    "ProductID": { S: "P1001" },
    "Stock": { N: "50" }
  }
}

conditionExpression = "Stock = :expectedStock"
ExpressionAttributeValues = { ":expectedStock": { N: "50" } }

TransactWriteItems {
  TransactItems: [
    {
      Update: {
        TableName: "Products",
        Key: { "ProductID": { S: "P1001" } },
        UpdateExpression: "SET Stock = :newStock",
        ConditionExpression: conditionExpression,
        ExpressionAttributeValues: {
          # Add both :newStock and :expectedStock here
        }
      }
    }
  ]
}

Need a hint?

Include both :newStock and :expectedStock in ExpressionAttributeValues.