Lambda function with DynamoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the AWS SDK for DynamoDB in a Lambda function.

DynamoDB

const AWS = require('[1]');

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

Aaws-sdk

Baws-sdk-client

Cdynamodb-sdk

Dlambda-sdk

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect package names like 'dynamodb-sdk' or 'lambda-sdk'.

Forgetting to import the AWS SDK before using DynamoDB.

The AWS SDK for JavaScript is imported using 'aws-sdk'. This allows access to DynamoDB and other AWS services.

2fill in blank

medium

Complete the code to create a DynamoDB DocumentClient instance in the Lambda function.

DynamoDB

const docClient = new AWS.[1]();

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ADynamoDBClient

BDocumentClient

CDynamoDB

DDynamoClient

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'DynamoDBClient' which is part of the newer AWS SDK v3, not v2.

Using 'DynamoDB' which is the low-level client, not the DocumentClient.

The DocumentClient simplifies working with DynamoDB by abstracting away low-level details. It is created with 'new AWS.DocumentClient()'.

3fill in blank

hard

Fix the error in the code to put an item into the DynamoDB table named 'Users'.

DynamoDB

const params = { TableName: 'Users', Item: [1] };
await docClient.put(params).promise();

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A'id: 123, name: Alice'

B[ id: 123, name: 'Alice' ]

C{ id: 123, name: 'Alice' }

Did=123, name='Alice'

Attempts:

3 left

💡 Hint

Common Mistakes

Using square brackets [] which define arrays, not objects.

Passing a string instead of an object for Item.

The Item must be an object with key-value pairs. Using curly braces { } defines an object. Square brackets or strings are invalid here.

4fill in blank

hard

Fill both blanks to get an item from the 'Products' table where the 'productId' equals '123'.

DynamoDB

const params = { TableName: '[1]', Key: { [2]: '123' } };
const data = await docClient.get(params).promise();

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AProducts

BproductId

CUsers

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong table name like 'Users'.

Using 'id' instead of 'productId' as the key attribute.

The TableName must be 'Products' and the Key attribute must be 'productId' to match the primary key of the table.

5fill in blank

hard

Fill all three blanks to update the 'status' attribute to 'active' for the item with 'userId' 'u123' in the 'Accounts' table.

DynamoDB

const params = {
  TableName: '[1]',
  Key: { [2]: 'u123' },
  UpdateExpression: 'set [3] = :s',
  ExpressionAttributeValues: { ':s': 'active' }
};
await docClient.update(params).promise();

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AAccounts

BuserId

Cstatus

DUsers

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong table name like 'Users'.

Using 'id' instead of 'userId' as the key.

Updating the wrong attribute name.

The TableName is 'Accounts', the Key attribute is 'userId', and the attribute to update is 'status'.

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