Why single-table design matters in DynamoDB - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the primary key attribute name in a DynamoDB table creation.

DynamoDB

KeySchema: [{ AttributeName: [1], KeyType: 'HASH' }]

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

AUsername

BUserId

CEmail

DTimestamp

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-unique attribute as the primary key.

Confusing sort key with partition key.

The primary key attribute name must be specified correctly to uniquely identify items. 'UserId' is a common choice for a partition key.

2fill in blank

medium

Complete the code to add a sort key attribute in the DynamoDB table schema.

DynamoDB

KeySchema: [ { AttributeName: 'UserId', KeyType: 'HASH' }, { AttributeName: [1], KeyType: 'RANGE' } ]

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

AStatus

BEmail

CUsername

DTimestamp

Attempts:

3 left

💡 Hint

Common Mistakes

Using an attribute that does not help sort items logically.

Omitting the sort key when multiple items per partition exist.

The sort key allows sorting and querying items with the same partition key. 'Timestamp' is commonly used to order events or records.

3fill in blank

hard

Fix the error in the query to fetch all items for a user using the partition key.

DynamoDB

const params = { TableName: 'Users', KeyConditionExpression: 'UserId = [1]', ExpressionAttributeValues: { ':uid': userId } };

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

A:uid

BuserId

CUserId

D?uid

Attempts:

3 left

💡 Hint

Common Mistakes

Using the attribute name directly instead of a placeholder.

Using a question mark instead of a colon for placeholders.

In DynamoDB queries, placeholders for values start with a colon ':' and must match keys in ExpressionAttributeValues.

4fill in blank

hard

Fill both blanks to create a DynamoDB update expression that sets a new attribute and increments a counter.

DynamoDB

UpdateExpression: 'SET [1] = :newVal, [2] = [2] + :inc'

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

ALastLogin

BLoginCount

CUserName

DStatus

Attempts:

3 left

💡 Hint

Common Mistakes

Using different attribute names for incrementing.

Forgetting to use the attribute name consistently.

The 'SET' clause updates 'LastLogin' to a new value and increments 'LoginCount' by a given amount.

5fill in blank

hard

Fill all three blanks to create a DynamoDB query that filters items by status and sorts by timestamp.

DynamoDB

const params = { TableName: 'Orders', KeyConditionExpression: '[1] = :userId', FilterExpression: '[2] = :status', ScanIndexForward: [3] };

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

AUserId

BOrderStatus

Ctrue

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong attribute names in expressions.

Confusing true and false for ScanIndexForward.

The query uses 'UserId' as the partition key, filters by 'OrderStatus', and sorts results in descending order (ScanIndexForward: false).

Practice

1. Why is single-table design important in DynamoDB?

easy

A. It requires more tables to organize data.

B. It stores related data together for faster access.

C. It increases the number of database calls.

D. It makes key design less important.

Solution

1. Step 1: Understand single-table design purpose

   Single-table design groups related data in one table to reduce complexity and speed up queries.

2. Step 2: Compare options with this purpose

   Only It stores related data together for faster access. correctly states it stores related data together for faster access.

3. Final Answer:

   It stores related data together for faster access. -> Option B

4. Quick Check:

   Single-table design = faster access [OK]

Hint: Single-table means fewer tables, faster queries [OK]

Common Mistakes:

• Thinking it increases database calls
• Believing it needs more tables
• Ignoring key design importance

2. Which of the following is the correct way to define a partition key in DynamoDB single-table design?

easy

A. PartitionKey: userId

B. PartitionKey: {userId, orderId}

C. PartitionKey: userId + orderId

D. PartitionKey: orderId

Solution

1. Step 1: Recall partition key definition

   The partition key must be a single attribute that uniquely partitions data.

2. Step 2: Analyze options

   PartitionKey: userId uses a single attribute userId, which is valid. PartitionKey: {userId, orderId} tries to use multiple attributes as one key, which is invalid syntax. PartitionKey: userId + orderId concatenates keys but is not a direct attribute definition. PartitionKey: orderId uses orderId alone, which may not be unique.

3. Final Answer:

   <code>PartitionKey: userId</code> -> Option A

4. Quick Check:

   Partition key = single attribute [OK]

Hint: Partition key must be a single attribute [OK]

Common Mistakes:

• Using multiple attributes directly as partition key
• Concatenating keys without defining attribute
• Choosing non-unique keys

3. Given a single-table design with partition key UserId and sort key OrderId, what will this query return?

SELECT * FROM Orders WHERE UserId = '123' AND OrderId = 'A1'

medium

A. All orders for user 123

B. All orders with OrderId 'A1' regardless of user

C. Only the order with OrderId 'A1' for user 123

D. Syntax error in query

Solution

1. Step 1: Understand key conditions in query

   The query filters by partition key UserId = '123' and sort key OrderId = 'A1', so it targets one specific item.

2. Step 2: Determine result based on keys

   Since both keys are specified, only the single matching order for user 123 with OrderId 'A1' will be returned.

3. Final Answer:

   Only the order with OrderId 'A1' for user 123 -> Option C

4. Quick Check:

   Partition + sort key = single item [OK]

Hint: Specify both keys to get one item [OK]

Common Mistakes:

• Assuming query returns all orders for user
• Ignoring sort key in query
• Thinking query syntax is invalid

4. You designed a single-table with partition key UserId and sort key OrderId. Your query to get all orders for a user returns no results, but you know data exists. What is the likely mistake?

medium

A. You queried only by sort key without partition key.

B. You used the wrong table name in the query.

C. You queried only by partition key without sort key.

D. You forgot to create the table.

Solution

1. Step 1: Recall query requirements for partition and sort keys

   In DynamoDB, queries must specify the partition key. Querying only by sort key is invalid and returns no results.

2. Step 2: Analyze options

   You queried only by sort key without partition key. matches the mistake of querying only by sort key. You used the wrong table name in the query. and D are possible but less likely if data exists. You queried only by partition key without sort key. is valid and returns all items with that partition key.

3. Final Answer:

   You queried only by sort key without partition key. -> Option A

4. Quick Check:

   Query must include partition key [OK]

Hint: Always include partition key in queries [OK]

Common Mistakes:

• Querying only by sort key
• Using wrong table name
• Assuming table not created

5. In a single-table design, you want to store both user profiles and their orders in one table. Which key design helps you efficiently query all orders for a user and also get the user profile quickly?

hard

A. Partition key: UserId#OrderId, Sort key: ItemType

B. Partition key: OrderId, Sort key: UserId

C. Partition key: ItemType, Sort key: UserId#OrderId

D. Partition key: UserId, Sort key: ItemType#OrderId

Solution

1. Step 1: Understand single-table design key patterns

   Using a partition key as UserId groups all user data together. Adding a sort key with ItemType#OrderId lets you separate user profile and orders.

2. Step 2: Evaluate options for efficient queries

   Partition key: UserId, Sort key: ItemType#OrderId allows querying all orders by filtering sort key starting with 'Order' and fetching profile with sort key 'Profile'. Other options mix keys making queries inefficient or impossible.

3. Final Answer:

   Partition key: UserId, Sort key: ItemType#OrderId -> Option D

4. Quick Check:

   Partition by user, sort by item type [OK]

Hint: Use partition key for user, sort key to separate items [OK]

Common Mistakes:

• Using orderId as partition key
• Not distinguishing item types in sort key
• Combining keys incorrectly