Basic scan operation in DynamoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to scan all items from the DynamoDB table named 'Products'.

DynamoDB

response = dynamodb_client.[1](TableName='Products')

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

Ascan

Bquery

Cget_item

Dput_item

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'query' instead of 'scan' will not return all items.

Using 'get_item' only fetches one item by key.

The scan operation reads all items in the table. Other operations like query or get_item are for specific keys or queries.

2fill in blank

medium

Complete the code to scan the 'Users' table and get only the 'UserId' and 'Email' attributes.

DynamoDB

response = dynamodb_client.scan(TableName='Users', ProjectionExpression='[1]')

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

AUserId; Email

BUserId Email

C'UserId, Email'

DUserId, Email

Attempts:

3 left

💡 Hint

Common Mistakes

Using spaces instead of commas between attribute names.

Adding quotes inside the string causing syntax errors.

The ProjectionExpression expects attribute names separated by commas without quotes.

3fill in blank

hard

Fix the error in the scan call to filter items where 'Status' equals 'Active'.

DynamoDB

response = dynamodb_client.scan(TableName='Orders', FilterExpression='[1] = :status', ExpressionAttributeValues={':status': {'S': 'Active'}})

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

A#Status

Bstatus

CStatus

D:Status

Attempts:

3 left

💡 Hint

Common Mistakes

Using ':Status' which is for values, not attribute names.

Using '#Status' without defining ExpressionAttributeNames.

The attribute name in FilterExpression should be the exact attribute name without prefix unless using expression attribute names.

4fill in blank

hard

Fill both blanks to scan the 'Employees' table and return only employees with 'Age' greater than 30.

DynamoDB

response = dynamodb_client.scan(TableName='Employees', FilterExpression='[1] > :age', ExpressionAttributeValues={':age': {'N': '[2]'}})

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

AAge

B30

CAgeGroup

D25

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong attribute name like 'AgeGroup'.

Using incorrect number value in ExpressionAttributeValues.

The filter expression uses the attribute name 'Age' and the value '30' to filter employees older than 30.

5fill in blank

hard

Fill all three blanks to scan the 'Books' table, projecting 'Title' and 'Author', and filtering books published after 2010.

DynamoDB

response = dynamodb_client.scan(TableName='Books', ProjectionExpression='[1], [2]', FilterExpression='[3] > :year', ExpressionAttributeValues={':year': {'N': '2010'}})

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

ATitle

BAuthor

CPublishedYear

DYear

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong attribute names in projection or filter.

Mixing attribute names with values.

The projection expression lists 'Title' and 'Author'. The filter expression uses 'PublishedYear' to filter books after 2010.

Practice

1. What does the scan operation do in DynamoDB?

easy

A. Reads all items in a table

B. Reads only one item by key

C. Deletes items from a table

D. Updates items in a table

Solution

1. Step 1: Understand the scan operation

   The scan operation reads every item in the DynamoDB table without filtering by key.

2. Step 2: Compare with other operations

   Unlike get or query, scan reads all items, not just specific keys.

3. Final Answer:

   Reads all items in a table -> Option A

4. Quick Check:

   Scan = Reads all items [OK]

Hint: Scan reads entire table, not just keys [OK]

Common Mistakes:

• Confusing scan with get or query
• Thinking scan deletes or updates data
• Assuming scan reads only filtered items

2. Which of the following is the correct syntax to perform a scan operation using AWS SDK for JavaScript v3?

easy

A. const data = await client.get({ TableName: 'MyTable' });

B. const data = await client.query({ TableName: 'MyTable' });

C. const data = await client.scan({ TableName: 'MyTable' });

D. const data = await client.delete({ TableName: 'MyTable' });

Solution

1. Step 1: Identify scan method usage

   The scan method is called on the DynamoDB client with parameters including TableName.

2. Step 2: Check other methods

   Get, query, and delete are different operations and do not perform scan.

3. Final Answer:

   const data = await client.scan({ TableName: 'MyTable' }); -> Option C

4. Quick Check:

   Scan syntax uses client.scan() [OK]

Hint: Scan uses client.scan() with TableName [OK]

Common Mistakes:

• Using get or query instead of scan
• Missing await keyword
• Wrong method names like delete

3. Given a DynamoDB table with 3 items: {id:1, name:'A'}, {id:2, name:'B'}, {id:3, name:'C'}, what will the scan operation return?

medium

A. [{id:1, name:'A'}, {id:2, name:'B'}, {id:3, name:'C'}]

B. Error: No items found

C. []

D. [{id:1, name:'A'}]

Solution

1. Step 1: Understand scan returns all items

   Scan reads every item in the table, so all 3 items will be returned.

2. Step 2: Check options for completeness

   Only [{id:1, name:'A'}, {id:2, name:'B'}, {id:3, name:'C'}] lists all 3 items; others are incomplete or errors.

3. Final Answer:

   [{id:1, name:'A'}, {id:2, name:'B'}, {id:3, name:'C'}] -> Option A

4. Quick Check:

   Scan returns all items [OK]

Hint: Scan returns full table items list [OK]

Common Mistakes:

• Expecting scan to return only one item
• Thinking scan returns empty if no filter
• Confusing scan with query results

4. You wrote this code to scan a DynamoDB table but get no results:

const params = { TableName: 'MyTable', FilterExpression: 'age > :val', ExpressionAttributeValues: { ':val': 30 } };
const data = await client.scan(params);

What is the likely problem?

medium

A. TableName is missing in params

B. FilterExpression syntax is incorrect, causing scan to fail

C. Scan does not support FilterExpression

D. FilterExpression is applied after scan reads all items, so no items match age > 30

Solution

1. Step 1: Understand FilterExpression in scan

   FilterExpression filters results after scanning all items; if no items match, result is empty.

2. Step 2: Check syntax and params

   Syntax is correct, TableName is present, and scan supports FilterExpression.

3. Final Answer:

   FilterExpression is applied after scan reads all items, so no items match age > 30 -> Option D

4. Quick Check:

   FilterExpression filters after scan [OK]

Hint: FilterExpression filters after scan reads all items [OK]

Common Mistakes:

• Thinking FilterExpression prevents scanning items
• Assuming scan fails with FilterExpression
• Missing TableName parameter

5. You want to scan a large DynamoDB table but only retrieve items where status is 'active'. Which approach is best to reduce data returned and improve performance?

hard

A. Use scan with FilterExpression 'status = :s' and ExpressionAttributeValues { ':s': 'active' }

B. Use query operation with status as partition key

C. Use scan without filters and filter results in application code

D. Use scan with ProjectionExpression to get only 'status' attribute

Solution

1. Step 1: Understand scan vs query

   Scan reads entire table; query reads items by key, more efficient for filtering.

2. Step 2: Check if status can be partition key

   If status is partition key, query can efficiently get only 'active' items without scanning all.

3. Step 3: Evaluate other options

   FilterExpression filters after scan, so less efficient; filtering in app wastes bandwidth; ProjectionExpression only limits attributes, not items.

4. Final Answer:

   Use query operation with status as partition key -> Option B

5. Quick Check:

   Query with key filters efficiently [OK]

Hint: Query by key is faster than scan with filters [OK]

Common Mistakes:

• Relying on scan with filters for large tables
• Filtering data in application instead of query
• Confusing ProjectionExpression with filtering items