Why DynamoDB pairs with Lambda - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a DynamoDB client in AWS Lambda.

DynamoDB

const AWS = require('aws-sdk');
const dynamoDB = new AWS.DynamoDB.[1]();

Drag options to blanks, or click blank then click option'

AService

BClient

CConnector

DDocumentClient

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Client' instead of 'DocumentClient' causes errors.

The DocumentClient is used in Lambda to interact easily with DynamoDB tables.

2fill in blank

medium

Complete the code to define a Lambda function that reads an item from DynamoDB.

DynamoDB

exports.handler = async (event) => {
  const params = {
    TableName: 'Users',
    Key: { 'UserId': event.[1] }
  };
  const data = await dynamoDB.get(params).promise();
  return data.Item;
};

Drag options to blanks, or click blank then click option'

AuserId

Bid

CUserId

Dkey

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'UserId' (case sensitive) instead of 'userId'.

The event object usually contains the user ID as userId to fetch the item.

3fill in blank

hard

Fix the error in the Lambda function that writes data to DynamoDB.

DynamoDB

exports.handler = async (event) => {
  const params = {
    TableName: 'Orders',
    Item: event.[1]
  };
  await dynamoDB.put(params).promise();
  return { statusCode: 200 };
};

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AItem

Bitem

Cdata

Dorder

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase 'item' causes the function to fail.

The put method requires the key Item with capital 'I' to specify the data.

4fill in blank

hard

Fill both blanks to create a Lambda function that deletes an item from DynamoDB using the correct key and method.

DynamoDB

exports.handler = async (event) => {
  const params = {
    TableName: 'Products',
    [1]: { 'ProductId': event.productId }
  };
  await dynamoDB.[2](params).promise();
  return { statusCode: 200 };
};

Drag options to blanks, or click blank then click option'

AKey

BItem

CdeleteItem

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Item' instead of 'Key' or 'deleteItem' instead of 'delete'.

The delete method deletes an item using the Key property to specify which item.

5fill in blank

hard

Fill the blanks to update an attribute in DynamoDB using Lambda.

DynamoDB

exports.handler = async (event) => {
  const params = {
    TableName: 'Employees',
    Key: { 'EmployeeId': event.employeeId },
    UpdateExpression: 'set [1] = :val',
    ExpressionAttributeValues: { ':val': event.newValue },
    ReturnValues: '{{BLANK_3}}'
  };
  const result = await dynamoDB.update(params).promise();
  return result.Attributes;
};

Drag options to blanks, or click blank then click option'

ASalary

BN

CUPDATED_NEW

DS

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong attribute name or wrong ReturnValues string.

To update the 'Salary' attribute, return 'UPDATED_NEW' to get updated attributes.

Practice

1. Why is DynamoDB often paired with AWS Lambda in serverless applications?

easy

A. Because Lambda can automatically run code when DynamoDB data changes

B. Because DynamoDB requires Lambda to store data

C. Because Lambda stores data faster than DynamoDB

D. Because DynamoDB and Lambda are both relational databases

Solution

1. Step 1: Understand DynamoDB's role

   DynamoDB stores data quickly and scales automatically without needing servers.

2. Step 2: Understand Lambda's role

   Lambda runs code automatically in response to events, such as changes in DynamoDB data.

3. Final Answer:

   Because Lambda can automatically run code when DynamoDB data changes -> Option A

4. Quick Check:

   Event-driven code execution = C [OK]

Hint: Remember: Lambda reacts to DynamoDB events automatically [OK]

Common Mistakes:

• Thinking DynamoDB needs Lambda to store data
• Confusing Lambda as a database
• Believing both are relational databases

2. Which of the following is the correct way to configure a Lambda function to trigger on DynamoDB table changes?

easy

A. Directly call Lambda from DynamoDB without any configuration

B. Set up a DynamoDB Stream and attach it as an event source to the Lambda function

C. Use Lambda to poll the DynamoDB table every second

D. Configure DynamoDB to run Lambda code inside its console

Solution

1. Step 1: Identify how DynamoDB triggers Lambda

   DynamoDB Streams capture table changes and can be linked to Lambda as event sources.

2. Step 2: Evaluate options

   Only setting up a DynamoDB Stream and attaching it to Lambda is correct; others are invalid or impossible.

3. Final Answer:

   Set up a DynamoDB Stream and attach it as an event source to the Lambda function -> Option B

4. Quick Check:

   DynamoDB Stream triggers Lambda = A [OK]

Hint: Use DynamoDB Streams to trigger Lambda functions [OK]

Common Mistakes:

• Assuming Lambda can be called directly by DynamoDB without streams
• Thinking Lambda polls DynamoDB instead of event-driven
• Believing DynamoDB runs Lambda code internally

3. Given this Lambda function triggered by a DynamoDB Stream event, what will be the output if a new item with {"id": "123", "status": "new"} is inserted?

exports.handler = async (event) => {
  for (const record of event.Records) {
    if (record.eventName === 'INSERT') {
      console.log('New item:', record.dynamodb.NewImage);
    }
  }
};

medium

A. Throws an error because NewImage is undefined

B. Does nothing because INSERT events are ignored

C. Logs only the id value as a string

D. Logs the new item data with keys and DynamoDB types

Solution

1. Step 1: Understand DynamoDB Stream event structure

   INSERT events include NewImage with the new item's attributes and their DynamoDB types.

2. Step 2: Analyze the Lambda code

   The code logs the NewImage object for INSERT events, so it outputs the full item with types.

3. Final Answer:

   Logs the new item data with keys and DynamoDB types -> Option D

4. Quick Check:

   INSERT event logs NewImage = B [OK]

Hint: INSERT events include NewImage with full item data [OK]

Common Mistakes:

• Assuming NewImage is undefined for INSERT
• Expecting only raw values without DynamoDB types
• Thinking INSERT events are ignored

4. A developer wrote this Lambda function to process DynamoDB Stream events but it never triggers. What is the likely issue?

exports.handler = async (event) => {
  console.log('Event received');
};

Options:

medium

A. The DynamoDB Stream is not enabled or not attached as an event source

B. The Lambda function code is missing a return statement

C. The function should use synchronous invocation instead of async

D. The console.log statement prevents the function from running

Solution

1. Step 1: Check event source configuration

   Lambda triggers on DynamoDB Streams only if the stream is enabled and linked as an event source.

2. Step 2: Evaluate code and invocation

   Code with async and console.log is valid; missing return or sync invocation does not stop triggering.

3. Final Answer:

   The DynamoDB Stream is not enabled or not attached as an event source -> Option A

4. Quick Check:

   Missing stream or event source = D [OK]

Hint: Check if DynamoDB Stream is enabled and linked to Lambda [OK]

Common Mistakes:

• Thinking async keyword blocks Lambda triggers
• Believing console.log stops execution
• Assuming return statement is required for triggers

5. You want to build a serverless app that updates a search index whenever DynamoDB data changes. Which approach best uses DynamoDB and Lambda together?

hard

A. Write search index updates directly inside DynamoDB using Lambda code embedded in the table

B. Have Lambda poll DynamoDB every minute to check for changes and update the index

C. Enable DynamoDB Streams, trigger Lambda on changes, and update the search index inside Lambda

D. Use DynamoDB triggers to run the search index update without Lambda

Solution

1. Step 1: Identify event-driven update method

   Using DynamoDB Streams to trigger Lambda on data changes is efficient and real-time.

2. Step 2: Evaluate alternatives

   Polling wastes resources, embedding code in DynamoDB is not possible, and DynamoDB triggers require Lambda.

3. Final Answer:

   Enable DynamoDB Streams, trigger Lambda on changes, and update the search index inside Lambda -> Option C

4. Quick Check:

   Event-driven updates with Streams + Lambda = A [OK]

Hint: Use Streams + Lambda for real-time updates, avoid polling [OK]

Common Mistakes:

• Choosing polling instead of event triggers
• Thinking DynamoDB can run code internally
• Ignoring the need for Lambda in triggers