Pagination with SDK in DynamoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to fetch the first page of items from a DynamoDB table using the SDK.

DynamoDB

const params = { TableName: 'Users', Limit: [1] };
const data = await dynamoDbClient.scan(params).promise();

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

Anull

B100

C0

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Setting Limit to 0 returns no items.

Using null for Limit causes an error.

The Limit parameter controls how many items are returned per page. Setting it to 10 fetches the first 10 items.

2fill in blank

medium

Complete the code to continue fetching the next page using the LastEvaluatedKey.

DynamoDB

const params = { TableName: 'Users', Limit: 10, ExclusiveStartKey: [1] };
const data = await dynamoDbClient.scan(params).promise();

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

Anull

Bdata.LastEvaluatedKey

Cundefined

D{}

Attempts:

3 left

💡 Hint

Common Mistakes

Passing null or undefined causes DynamoDB to start from the beginning.

Using an empty object {} does not work as a start key.

The ExclusiveStartKey tells DynamoDB where to start the next page. Use data.LastEvaluatedKey from the previous response.

3fill in blank

hard

Fix the error in the code to correctly check if there are more pages to fetch.

DynamoDB

if (data.[1]) {
  // fetch next page
}

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

AMoreResults

BNextPageKey

CLastEvaluatedKey

DHasNext

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect property names like NextPageKey or HasNext.

Checking for a boolean instead of the key object.

The DynamoDB SDK uses LastEvaluatedKey to indicate if more pages exist.

4fill in blank

hard

Fill both blanks to correctly set up the scan parameters for paginated fetching.

DynamoDB

const params = { TableName: 'Orders', Limit: [1], ExclusiveStartKey: [2] };
const data = await dynamoDbClient.scan(params).promise();

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

A20

Bdata.LastEvaluatedKey

Cnull

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Using data.LastEvaluatedKey on the first page causes errors.

Setting Limit too high or zero.

Set Limit to 20 to fetch 20 items per page. Use null for ExclusiveStartKey on the first page.

5fill in blank

hard

Fill all three blanks to build a loop that fetches all pages from a DynamoDB table.

DynamoDB

let lastKey = [1];
do {
  const params = { TableName: 'Products', Limit: [2], ExclusiveStartKey: lastKey };
  const data = await dynamoDbClient.scan(params).promise();
  // process data.Items
  lastKey = data.[3];
} while (lastKey);

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

Anull

B50

CLastEvaluatedKey

Dundefined

Attempts:

3 left

💡 Hint

Common Mistakes

Starting lastKey as undefined causes errors.

Not updating lastKey inside the loop.

Using wrong property name for the next key.

Initialize lastKey as null to start from the beginning. Set Limit to 50 items per page. Update lastKey with data.LastEvaluatedKey to continue paging.

Practice

1. What does the Limit parameter do when paginating results in DynamoDB SDK?

easy

A. It specifies the starting point for the next page.

B. It sets the maximum number of items returned in one page.

C. It filters items based on a condition.

D. It sorts the results in ascending order.

Solution

1. Step 1: Understand the role of Limit in pagination

   The Limit parameter controls how many items DynamoDB returns in a single request, effectively setting the page size.

2. Step 2: Differentiate from other parameters

   ExclusiveStartKey sets the starting point for the next page, not Limit. Filtering and sorting are handled differently.

3. Final Answer:

   It sets the maximum number of items returned in one page. -> Option B

4. Quick Check:

   Limit = page size [OK]

Hint: Limit controls page size, not start or filter [OK]

Common Mistakes:

• Confusing Limit with ExclusiveStartKey
• Thinking Limit filters data
• Assuming Limit sorts results

2. Which of the following is the correct way to continue fetching the next page of results in DynamoDB SDK?

easy

A. Set StartKey to zero.

B. Use Limit with the last item key.

C. Set ExclusiveStartKey to the last evaluated key from previous response.

D. Use NextPageToken parameter.

Solution

1. Step 1: Identify the parameter for pagination continuation

   DynamoDB uses ExclusiveStartKey to tell the query where to start for the next page.

2. Step 2: Verify other options

   Limit sets page size, StartKey is not a valid parameter, and NextPageToken is not used in DynamoDB SDK.

3. Final Answer:

   Set ExclusiveStartKey to the last evaluated key from previous response. -> Option C

4. Quick Check:

   Use ExclusiveStartKey for next page [OK]

Hint: Use ExclusiveStartKey to continue pagination [OK]

Common Mistakes:

• Using Limit to continue pages
• Using invalid parameter StartKey
• Assuming NextPageToken exists in DynamoDB

3. Given the following DynamoDB SDK code snippet, what will be the output if LastEvaluatedKey is not empty?

const params = { TableName: 'Books', Limit: 2 };
const data = await dynamoDbClient.scan(params);
console.log(data.Items.length);
console.log(data.LastEvaluatedKey !== undefined);

medium

A. Error due to missing ExclusiveStartKey

B. All items and false

C. 2 and false

D. 2 and true

Solution

1. Step 1: Understand Limit effect on Items returned

   With Limit: 2, the scan returns at most 2 items, so data.Items.length will be 2.

2. Step 2: Check LastEvaluatedKey presence

   If LastEvaluatedKey is not empty, it means more pages exist, so data.LastEvaluatedKey !== undefined is true.

3. Final Answer:

   2 and true -> Option D

4. Quick Check:

   Limit = 2 items, LastEvaluatedKey present = true [OK]

Hint: Limit caps items; LastEvaluatedKey true means more pages [OK]

Common Mistakes:

• Assuming all items returned ignoring Limit
• Thinking LastEvaluatedKey is false when present
• Expecting error without ExclusiveStartKey

4. You wrote this code to paginate DynamoDB scan results but it returns only the first page repeatedly:

let params = { TableName: 'Users', Limit: 3 };
let data;
do {
  data = await dynamoDbClient.scan(params);
  console.log(data.Items);
} while (data.LastEvaluatedKey);

What is the main issue?

medium

A. Missing update of ExclusiveStartKey in params inside the loop.

B. Limit should be increased to fetch all items.

C. The loop condition should check data.Items instead.

D. The scan method does not support pagination.

Solution

1. Step 1: Analyze loop behavior

   The code calls scan repeatedly but never updates ExclusiveStartKey, so it fetches the same first page each time.

2. Step 2: Identify correct fix

   To get next pages, params.ExclusiveStartKey must be set to data.LastEvaluatedKey inside the loop.

3. Final Answer:

   Missing update of ExclusiveStartKey in params inside the loop. -> Option A

4. Quick Check:

   Update ExclusiveStartKey to paginate [OK]

Hint: Update ExclusiveStartKey each loop to get next page [OK]

Common Mistakes:

• Not updating ExclusiveStartKey inside loop
• Increasing Limit instead of paginating
• Wrong loop condition on Items
• Thinking scan can't paginate

5. You want to fetch all items from a large DynamoDB table using pagination with the SDK. Which approach correctly handles this scenario?

hard

A. Use a loop that calls scan with Limit, updating ExclusiveStartKey each time until LastEvaluatedKey is undefined.

B. Call scan once with a very large Limit to get all items at once.

C. Use scan without Limit and stop when Items array is empty.

D. Call scan repeatedly without ExclusiveStartKey until Items length is zero.

Solution

1. Step 1: Understand DynamoDB pagination for large tables

   Large tables require multiple scan calls with a Limit to avoid timeouts and memory issues.

2. Step 2: Correctly implement pagination loop

   Each scan call should use ExclusiveStartKey from the previous LastEvaluatedKey until it is undefined, indicating no more pages.

3. Final Answer:

   Use a loop that calls scan with Limit, updating ExclusiveStartKey each time until LastEvaluatedKey is undefined. -> Option A

4. Quick Check:

   Loop with Limit and ExclusiveStartKey until done [OK]

Hint: Loop with Limit and ExclusiveStartKey until no LastEvaluatedKey [OK]

Common Mistakes:

• Using huge Limit causing timeouts
• Ignoring ExclusiveStartKey for next pages
• Stopping on empty Items instead of LastEvaluatedKey
• Calling scan repeatedly without pagination