Lambda function with DynamoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the role of an AWS Lambda function when working with DynamoDB?

An AWS Lambda function runs code in response to events and can read from or write to DynamoDB tables without managing servers.

beginner

How do you write data to a DynamoDB table inside a Lambda function?

You use the AWS SDK inside the Lambda function to call DynamoDB's PutItem or UpdateItem API to add or modify data.

intermediate

What is the purpose of the event parameter in a Lambda function triggered by DynamoDB?

The event parameter contains information about the DynamoDB data change that triggered the Lambda, such as inserted or updated items.

intermediate

Why is it important to set proper IAM permissions for a Lambda function accessing DynamoDB?

IAM permissions control what the Lambda function can do with DynamoDB, ensuring it only accesses allowed tables and operations for security.

intermediate

What is a common use case for combining Lambda functions with DynamoDB streams?

A common use case is to automatically process or react to data changes in DynamoDB, like sending notifications or updating other systems.

What AWS service lets you run code without managing servers and can interact with DynamoDB?

A Amazon S3

B Amazon EC2

C AWS Lambda

D AWS CloudFormation

AWS Lambda runs code in response to events without needing servers and can access DynamoDB.

Which DynamoDB API call is used to add a new item inside a Lambda function?

A GetItem

B PutItem

C DeleteItem

D Scan

PutItem adds a new item or replaces an existing item in a DynamoDB table.

What does a DynamoDB stream provide to a Lambda function?

A A record of data changes

B A list of all tables

C A backup of the table

D User access logs

DynamoDB streams capture data changes like inserts, updates, and deletes for Lambda to process.

Which AWS feature controls what actions a Lambda function can perform on DynamoDB?

A IAM roles and policies

B VPC

C CloudWatch

D SNS

IAM roles and policies define permissions for Lambda to access DynamoDB securely.

What is a typical reason to trigger a Lambda function from a DynamoDB stream?

A To create a new DynamoDB table

B To backup data manually

C To delete the DynamoDB table

D To process data changes automatically

Lambda functions triggered by streams can automatically react to data changes for processing or notifications.

Explain how a Lambda function can interact with DynamoDB to handle data changes.

Think about how Lambda reacts to data updates and uses the event info.

Describe the importance of IAM permissions when using Lambda with DynamoDB.

Consider why security matters when Lambda talks to DynamoDB.

Practice

1. What is the main purpose of using a Lambda function with DynamoDB in AWS?

easy

A. To run code automatically when DynamoDB data changes

B. To manually update DynamoDB tables from the AWS console

C. To create new DynamoDB tables without coding

D. To backup DynamoDB data to S3 manually

Solution

1. Step 1: Understand Lambda triggers

   Lambda functions can be triggered by events, such as changes in DynamoDB tables.

2. Step 2: Identify the purpose of automation

   This allows automatic code execution when data changes, without manual intervention.

3. Final Answer:

   To run code automatically when DynamoDB data changes -> Option A

4. Quick Check:

   Lambda triggers = automatic code run [OK]

Hint: Lambda runs code on events like DynamoDB changes [OK]

Common Mistakes:

• Thinking Lambda manually updates tables
• Confusing Lambda with backup tools
• Assuming Lambda creates tables automatically

2. Which of the following is the correct way to initialize AWS DynamoDB DocumentClient in a Node.js Lambda function?

easy

A. const docClient = new AWS.DynamoDBClient();

B. const docClient = new AWS.DynamoDB.DocumentClient();

C. const docClient = AWS.DynamoDB.DocumentClient();

D. const docClient = AWS.DynamoDB.Document();

Solution

1. Step 1: Recall correct DocumentClient syntax

   The AWS SDK requires using 'new' keyword to create a DocumentClient instance.

2. Step 2: Match correct class name and usage

   The correct class is AWS.DynamoDB.DocumentClient, not DynamoDBClient or Document.

3. Final Answer:

   const docClient = new AWS.DynamoDB.DocumentClient(); -> Option B

4. Quick Check:

   Use 'new' with DocumentClient class [OK]

Hint: Use 'new AWS.DynamoDB.DocumentClient()' to initialize [OK]

Common Mistakes:

• Omitting 'new' keyword
• Using wrong class name like DynamoDBClient
• Calling Document() instead of DocumentClient

3. Given this Lambda function snippet, what will be the output if the item with id '123' exists in the DynamoDB table?

const AWS = require('aws-sdk');
const docClient = new AWS.DynamoDB.DocumentClient();

exports.handler = async (event) => {
  const params = {
    TableName: 'Users',
    Key: { id: '123' }
  };
  const data = await docClient.get(params).promise();
  return data.Item;
};

medium

A. An error because 'get' method is incorrect

B. A list of all items in the Users table

C. An empty object {}

D. The item object with id '123' from the Users table

Solution

1. Step 1: Understand docClient.get usage

   The get method retrieves a single item by key from the specified table.

2. Step 2: Analyze the return value

   If the item with id '123' exists, data.Item will contain that item object.

3. Final Answer:

   The item object with id '123' from the Users table -> Option D

4. Quick Check:

   docClient.get returns item if found [OK]

Hint: docClient.get returns single item by key [OK]

Common Mistakes:

• Expecting a list instead of single item
• Thinking get method is invalid
• Assuming empty object if item exists

4. Identify the error in this Lambda function code that writes an item to DynamoDB:

const AWS = require('aws-sdk');
const docClient = new AWS.DynamoDB.DocumentClient();

exports.handler = async (event) => {
  const params = {
    TableName: 'Products',
    Item: {
      productId: '001',
      name: 'Book'
    }
  };
  await docClient.putItem(params).promise();
  return 'Success';
};

medium

A. Using 'putItem' instead of 'put' method on DocumentClient

B. Missing 'Key' property in params

C. TableName should be lowercase

D. Missing callback function in putItem

Solution

1. Step 1: Check DocumentClient method names

   DocumentClient uses 'put' method, not 'putItem'.

2. Step 2: Confirm correct method usage

   Using 'putItem' causes a runtime error because it does not exist on DocumentClient.

3. Final Answer:

   Using 'putItem' instead of 'put' method on DocumentClient -> Option A

4. Quick Check:

   Use 'put' to write items with DocumentClient [OK]

Hint: Use 'put', not 'putItem', with DocumentClient [OK]

Common Mistakes:

• Confusing low-level DynamoDB client with DocumentClient
• Assuming 'putItem' exists in DocumentClient
• Ignoring method naming conventions

5. You want a Lambda function to update a user's email in DynamoDB only if the user exists. Which approach correctly ensures this conditional update?

hard

A. Use docClient.delete before updating

B. Use docClient.put without any condition

C. Use docClient.update with ConditionExpression 'attribute_exists(id)'

D. Use docClient.get and then docClient.put unconditionally

Solution

1. Step 1: Understand conditional update in DynamoDB

   To update only if an item exists, use ConditionExpression with 'attribute_exists' on the key.

2. Step 2: Apply ConditionExpression in update method

   docClient.update supports ConditionExpression to prevent overwriting non-existing items.

3. Step 3: Evaluate other options

   Using put without condition overwrites or creates new items; delete before update is inefficient; get then put is not atomic.

4. Final Answer:

   Use docClient.update with ConditionExpression 'attribute_exists(id)' -> Option C

5. Quick Check:

   Conditional update = update + attribute_exists [OK]

Hint: Use ConditionExpression 'attribute_exists' for safe updates [OK]

Common Mistakes:

• Using put which overwrites without condition
• Deleting item before update unnecessarily
• Not using atomic conditional update