Query by partition key in DynamoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to query items by partition key in DynamoDB.

DynamoDB

response = table.query(KeyConditionExpression=Key('[1]').eq('123'))

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

AEmail

BSortKey

CTimestamp

DUserId

Attempts:

3 left

💡 Hint

Common Mistakes

Using the sort key instead of the partition key in the query condition.

Using an attribute name that does not exist in the table schema.

The partition key attribute name must be used in the KeyConditionExpression to query items correctly.

2fill in blank

medium

Complete the code to query items with a specific partition key value using boto3.

DynamoDB

response = table.query(KeyConditionExpression=Key('UserId').eq([1]))

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

A"User123"

B'123'

C123

DUser123

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the key value without quotes causing a syntax error.

Using variable names instead of string literals.

The partition key value must be a string enclosed in quotes when passed to the eq() method.

3fill in blank

hard

Fix the error in the query code to correctly use the partition key.

DynamoDB

response = table.query(KeyConditionExpression=Key('[1]').eq('abc'))

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

AUserId

BSortKey

CPartitionKey

DTimestamp

Attempts:

3 left

💡 Hint

Common Mistakes

Using a generic name like 'PartitionKey' which is not the actual attribute name.

Confusing partition key with sort key attribute names.

The partition key attribute name must be used exactly as defined in the table schema, here 'UserId'.

4fill in blank

hard

Fill both blanks to query items by partition key and sort key condition.

DynamoDB

response = table.query(KeyConditionExpression=Key('[1]').eq('user1') & Key('[2]').begins_with('2023'))

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

AUserId

BTimestamp

CSortKey

DEmail

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping partition key and sort key names.

Using attribute names not defined in the table.

The partition key is 'UserId' and the sort key is 'SortKey'. The query filters items where UserId equals 'user1' and SortKey begins with '2023'.

5fill in blank

hard

Fill all three blanks to query items by partition key and filter results by an attribute.

DynamoDB

response = table.query(KeyConditionExpression=Key('[1]').eq('user42'), FilterExpression=Attr('[2]').[3]('active'))

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

AUserId

BStatus

Ceq

Dbegins_with

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'begins_with' instead of 'eq' in the filter expression.

Using wrong attribute names for partition key or filter.

The partition key is 'UserId'. The filter expression checks if the 'Status' attribute equals 'active'.

Practice

1. What does querying by partition key in DynamoDB do?

easy

A. Updates all items with the same partition key value

B. Deletes all items with the same partition key value

C. Fetches all items with the same partition key value

D. Creates a new item with the partition key value

Solution

1. Step 1: Understand partition key role

   The partition key uniquely identifies the partition where items are stored.

2. Step 2: Query by partition key fetches items

   Querying by partition key returns all items that share that key value.

3. Final Answer:

   Fetches all items with the same partition key value -> Option C

4. Quick Check:

   Query by partition key = fetch items [OK]

Hint: Partition key query fetches matching items only [OK]

Common Mistakes:

• Thinking it deletes or updates items
• Confusing partition key with sort key
• Assuming it creates new items

2. Which of the following is the correct syntax to query items by partition key 'UserID' with value '123' in DynamoDB?

easy

A. Table.query(KeyConditionExpression: 'UserID = 123')

B. Table.query(KeyConditionExpression: 'UserID = :val', ExpressionAttributeValues: {':val': '123'})

C. Table.query(FilterExpression: 'UserID = 123')

D. Table.query(KeyConditionExpression: 'UserID == 123')

Solution

1. Step 1: Identify correct query syntax

   DynamoDB requires KeyConditionExpression with placeholders and ExpressionAttributeValues.

2. Step 2: Check each option

   Table.query(KeyConditionExpression: 'UserID = :val', ExpressionAttributeValues: {':val': '123'}) uses correct syntax with placeholder ':val' and value mapping. Others misuse operators or omit placeholders.

3. Final Answer:

   Table.query(KeyConditionExpression: 'UserID = :val', ExpressionAttributeValues: {':val': '123'}) -> Option B

4. Quick Check:

   Use placeholders and ExpressionAttributeValues [OK]

Hint: Use placeholders (:val) and ExpressionAttributeValues [OK]

Common Mistakes:

• Using '==' instead of '=' in KeyConditionExpression
• Not using ExpressionAttributeValues for values
• Using FilterExpression instead of KeyConditionExpression

3. Given a DynamoDB table with items: {UserID: '123', Name: 'Alice'}, {UserID: '123', Name: 'Bob'}, {UserID: '456', Name: 'Carol'}, what will the query by partition key 'UserID' = '123' return?

medium

A. [{UserID: '123', Name: 'Alice'}, {UserID: '123', Name: 'Bob'}]

B. [{UserID: '456', Name: 'Carol'}]

C. [{UserID: '123', Name: 'Alice'}]

D. [] (empty list)

Solution

1. Step 1: Identify items with partition key '123'

   Items with UserID '123' are Alice and Bob.

2. Step 2: Query returns all matching items

   Query returns both Alice and Bob items as they share the partition key.

3. Final Answer:

   [{UserID: '123', Name: 'Alice'}, {UserID: '123', Name: 'Bob'}] -> Option A

4. Quick Check:

   Query by '123' returns Alice and Bob [OK]

Hint: Query returns all items with matching partition key [OK]

Common Mistakes:

• Expecting only one item returned
• Confusing partition key with sort key filtering
• Assuming query returns items with different partition keys

4. You wrote this query to get items with partition key 'OrderID' = '789': Table.query(KeyConditionExpression: 'OrderID = 789'). It returns an error. What is the problem?

medium

A. Partition key name is case-sensitive and should be 'orderid'

B. Using wrong operator '==' instead of '='

C. Query method does not support KeyConditionExpression

D. Missing ExpressionAttributeValues for the value '789'

Solution

1. Step 1: Check query syntax requirements

   DynamoDB requires placeholders and ExpressionAttributeValues for values in KeyConditionExpression.

2. Step 2: Identify missing part

   The query uses 'OrderID = 789' directly without placeholder or ExpressionAttributeValues, causing error.

3. Final Answer:

   Missing ExpressionAttributeValues for the value '789' -> Option D

4. Quick Check:

   Use placeholders and ExpressionAttributeValues [OK]

Hint: Always use placeholders and ExpressionAttributeValues [OK]

Common Mistakes:

• Using raw values instead of placeholders
• Assuming case-insensitivity for partition key
• Using '==' operator instead of '='

5. You want to query a DynamoDB table for all items with partition key 'Category' = 'Books' and sort key 'Price' less than 20. Which approach correctly uses query by partition key with a condition on sort key?

hard

A. Use KeyConditionExpression: 'Category = :cat AND Price < :price' with ExpressionAttributeValues {':cat': 'Books', ':price': 20}

B. Use FilterExpression: 'Category = :cat AND Price < :price' with ExpressionAttributeValues {':cat': 'Books', ':price': 20}

C. Use KeyConditionExpression: 'Category = :cat' and FilterExpression: 'Price < :price' with ExpressionAttributeValues {':cat': 'Books', ':price': 20}

D. Use FilterExpression: 'Category = :cat' and KeyConditionExpression: 'Price < :price' with ExpressionAttributeValues {':cat': 'Books', ':price': 20}

Solution

1. Step 1: Understand query conditions

   KeyConditionExpression must include partition key equality and supports sort key conditions like <. FilterExpression filters results after the query.

2. Step 2: Analyze options

   Use KeyConditionExpression: 'Category = :cat AND Price < :price' with ExpressionAttributeValues {':cat': 'Books', ':price': 20} correctly uses KeyConditionExpression: 'Category = :cat AND Price < :price', which efficiently queries the partition with a sort key range condition. Use KeyConditionExpression: 'Category = :cat' and FilterExpression: 'Price < :price' with ExpressionAttributeValues {':cat': 'Books', ':price': 20} uses FilterExpression for Price (valid but less efficient). B lacks KeyConditionExpression. D omits partition key from KeyConditionExpression.

3. Final Answer:

   Use KeyConditionExpression: 'Category = :cat AND Price < :price' with ExpressionAttributeValues {':cat': 'Books', ':price': 20} -> Option A

4. Quick Check:

   KeyConditionExpression: partition = AND sort < [OK]

Hint: KeyConditionExpression: partition = AND sort condition [OK]

Common Mistakes:

• Using FilterExpression for partition key
• Using FilterExpression instead of KeyConditionExpression for sort key range
• Mixing KeyConditionExpression and FilterExpression incorrectly