Limit and pagination in DynamoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to limit the number of items returned to 5.

DynamoDB

response = table.scan(Limit=[1])

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

A0

B10

C5

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using a number larger than needed.

Setting Limit to 0 which returns no items.

The Limit parameter controls how many items DynamoDB returns in one call. Setting it to 5 returns only 5 items.

2fill in blank

medium

Complete the code to start scanning from the last evaluated key stored in last_key.

DynamoDB

response = table.scan(ExclusiveStartKey=[1])

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

Alast_key

B{}

CNone

Dstart_key

Attempts:

3 left

💡 Hint

Common Mistakes

Passing None which means start from the beginning.

Using a wrong variable name.

The ExclusiveStartKey parameter tells DynamoDB where to continue scanning from. You pass the last key you got from the previous scan.

3fill in blank

hard

Fix the error in the code to correctly check if there are more items to scan.

DynamoDB

if 'LastEvaluatedKey' in response and response[1] 'LastEvaluatedKey' is not None:
    last_key = response['LastEvaluatedKey']

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

Ais

B==

Cnot in

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using == which checks equality, not inequality.

Using is which is not correct for this check.

You want to check that LastEvaluatedKey exists and is not None. Using != correctly tests that.

4fill in blank

hard

Fill both blanks to scan with a limit of 10 and start from the last evaluated key.

DynamoDB

response = table.scan(Limit=[1], ExclusiveStartKey=[2])

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

A10

Blast_key

C5

D{}

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong limit values.

Not passing the correct start key variable.

Set Limit to 10 to get 10 items per scan, and use last_key to continue from where the last scan ended.

5fill in blank

hard

Fill all three blanks to create a loop that paginates through all items with a limit of 3.

DynamoDB

last_key = None
items = []
while True:
    response = table.scan(Limit=[1], ExclusiveStartKey=[2])
    items.extend(response['Items'])
    if 'LastEvaluatedKey' not in response or response['LastEvaluatedKey'] is None:
        break
    last_key = response[[3]]

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

A3

Blast_key

C'LastEvaluatedKey'

D'Items'

Attempts:

3 left

💡 Hint

Common Mistakes

Not updating last_key correctly.

Using wrong keys or limit values.

This loop scans the table in pages of 3 items. It uses last_key to continue scanning and stops when no more keys are returned.

Practice

1. What does the Limit parameter do in a DynamoDB query or scan?

easy

A. It filters items based on a condition.

B. It sets the maximum size of each item returned.

C. It limits the number of items returned in one response.

D. It sorts the items in ascending order.

Solution

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

   The Limit parameter controls how many items DynamoDB returns in a single query or scan response.

2. Step 2: Differentiate Limit from other parameters

   Limit does not filter or sort items; it only restricts the count of items returned at once.

3. Final Answer:

   It limits the number of items returned in one response. -> Option C

4. Quick Check:

   Limit = number of items returned [OK]

Hint: Limit sets max items per response, not filtering or sorting [OK]

Common Mistakes:

• Confusing Limit with filtering conditions
• Thinking Limit sorts the results
• Assuming Limit changes item size

2. Which of the following is the correct way to specify a limit of 5 items in a DynamoDB query using AWS SDK for JavaScript?

easy

A. query({ TableName: 'MyTable', MaxResults: 5 })

B. query({ TableName: 'MyTable', Limit: 5 })

C. query({ TableName: 'MyTable', MaxItems: 5 })

D. query({ TableName: 'MyTable', limit: 5 })

Solution

1. Step 1: Check parameter case sensitivity in AWS SDK

   In AWS SDK for JavaScript, parameter names are case-sensitive and 'Limit' must be capitalized.

2. Step 2: Verify correct parameter name for limiting items

   The correct parameter to limit items is 'Limit', not 'limit', 'MaxItems', or 'MaxResults'.

3. Final Answer:

   query({ TableName: 'MyTable', Limit: 5 }) -> Option B

4. Quick Check:

   Correct case and name for limit is 'Limit' [OK]

Hint: Use exact 'Limit' with capital L in query parameters [OK]

Common Mistakes:

• Using lowercase 'limit' instead of 'Limit'
• Using wrong parameter names like MaxItems
• Confusing limit with max results

3. Given a DynamoDB table with 10 items, what will be the result of this scan operation?

scan({ TableName: 'MyTable', Limit: 3 })

medium

A. Returns all 10 items in one response.

B. Returns exactly 3 items in the response.

C. Returns an error because Limit is too small.

D. Returns 3 items and a LastEvaluatedKey for next page.

Solution

1. Step 1: Understand Limit effect on scan results

   Limit restricts the number of items returned in one response to 3.

2. Step 2: Recognize pagination behavior with LastEvaluatedKey

   Since there are more items (10 total), DynamoDB returns 3 items plus a LastEvaluatedKey to continue scanning next items.

3. Final Answer:

   Returns 3 items and a LastEvaluatedKey for next page. -> Option D

4. Quick Check:

   Limit 3 + more items = partial results + LastEvaluatedKey [OK]

Hint: Limit returns partial items plus LastEvaluatedKey if more exist [OK]

Common Mistakes:

• Assuming all items return ignoring Limit
• Thinking Limit causes error if small
• Missing LastEvaluatedKey for pagination

4. You run this DynamoDB query but get an error:

query({ TableName: 'MyTable', Limit: 5, ExclusiveStartKey: { id: '123' } })

What is the most likely cause?

medium

A. ExclusiveStartKey is missing required key attributes.

B. Limit cannot be used with ExclusiveStartKey.

C. TableName is incorrect.

D. Limit value must be greater than 10.

Solution

1. Step 1: Understand ExclusiveStartKey requirements

   ExclusiveStartKey must include the full primary key attributes exactly as stored in the table.

2. Step 2: Identify error cause

   If the provided ExclusiveStartKey lacks required key attributes or has wrong format, DynamoDB returns an error.

3. Final Answer:

   ExclusiveStartKey is missing required key attributes. -> Option A

4. Quick Check:

   ExclusiveStartKey needs full primary key [OK]

Hint: ExclusiveStartKey must have full primary key attributes [OK]

Common Mistakes:

• Thinking Limit and ExclusiveStartKey cannot be combined
• Assuming TableName typo causes this error
• Believing Limit must be > 10

5. You want to fetch all items from a large DynamoDB table but only 4 items at a time to avoid timeouts. Which approach correctly implements pagination?

hard

A. Use Limit: 4 and pass LastEvaluatedKey from previous response as ExclusiveStartKey in next query.

B. Use Limit: 4 and always start query with ExclusiveStartKey: null.

C. Use Limit: 4 and increase Limit by 4 each time to get next items.

D. Use Limit: 4 and scan the whole table once without ExclusiveStartKey.

Solution

1. Step 1: Understand pagination with Limit and ExclusiveStartKey

   Limit controls how many items are returned per request. To get next items, use ExclusiveStartKey with LastEvaluatedKey from previous response.

2. Step 2: Confirm correct pagination process

   Use Limit: 4 and pass LastEvaluatedKey from previous response as ExclusiveStartKey in next query to fetch items in pages. Restarting from the beginning, increasing Limit, or scanning without pagination leads to repeated or incomplete results.

3. Final Answer:

   Use Limit: 4 and pass LastEvaluatedKey from previous response as ExclusiveStartKey in next query. -> Option A

4. Quick Check:

   Pagination = Limit + ExclusiveStartKey chaining [OK]

Hint: Pass LastEvaluatedKey as ExclusiveStartKey to paginate [OK]

Common Mistakes:

• Restarting query without ExclusiveStartKey
• Increasing Limit instead of paginating
• Scanning whole table ignoring pagination