Tables, items, and attributes in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding DynamoDB Table Keys

In AWS DynamoDB, what is the primary difference between a partition key and a sort key in a table?

A Partition key determines the partition for each item, while sort key allows multiple items with the same partition key but different sort keys.

B Sort key uniquely identifies each item, while partition key allows multiple items with the same sort key but different partition keys.

C Partition key and sort key both must be unique across the entire table.

D Partition key is optional, but sort key is mandatory for all tables.

💡 Hint

Think about how DynamoDB organizes data to allow efficient queries.

The partition key determines the partition where data is stored. The sort key allows multiple items to share the same partition key but be distinguished by the sort key.

❓ Configuration

intermediate

DynamoDB Item Attribute Types

Which of the following JSON representations correctly defines a DynamoDB item with a string attribute 'Name' and a number attribute 'Age'?

A {"Name": "Alice", "Age": 30}

B {"Name": {"SS": ["Alice"]}, "Age": {"NS": ["30"]}}

C {"Name": {"N": "Alice"}, "Age": {"S": "30"}}

D {"Name": {"S": "Alice"}, "Age": {"N": "30"}}

💡 Hint

DynamoDB expects attribute values to be typed explicitly in JSON format.

DynamoDB JSON format requires attribute values to be objects with a type key such as 'S' for string and 'N' for number, with the value as a string.

❓ Architecture

advanced

Designing a DynamoDB Table for High Write Throughput

You need to design a DynamoDB table to handle very high write throughput evenly distributed across partitions. Which table key design helps avoid hot partitions?

A Use only a sort key without a partition key.

B Use a partition key with sequential numeric values.

C Use a composite key with a high-cardinality partition key and a sort key.

D Use a simple partition key with low cardinality values.

💡 Hint

Think about how DynamoDB partitions data and distributes load.

A high-cardinality partition key spreads writes across many partitions, preventing hot spots. A composite key with a sort key allows efficient queries and balanced writes.

❓ security

advanced

Controlling Access to Specific Attributes in DynamoDB

How can you restrict a user’s access to only certain attributes of items in a DynamoDB table?

A Use IAM policies with condition keys to allow access only to specific attributes.

B Create a separate table with only the allowed attributes and give access to that table.

C Use DynamoDB Streams to filter attributes before access.

D Encrypt the attributes you want to restrict.

💡 Hint

Consider AWS IAM fine-grained access control features.

IAM policies can use condition keys like dynamodb:Attributes to restrict access to specific attributes within items.

❓ service_behavior

expert

DynamoDB Consistency Model Impact on Reads

If you perform a strongly consistent read on a DynamoDB table immediately after writing an item, what is the expected behavior?

A The read may return stale data due to eventual consistency.

B The read always returns the latest written data.

C The read will fail if the write is not yet fully replicated.

D The read returns data only if the item has a sort key.

💡 Hint

Think about the difference between eventually consistent and strongly consistent reads.

Strongly consistent reads always return the most recent data after a successful write, ensuring no stale data is returned.

Practice

1. What is the main purpose of a table in AWS DynamoDB?

easy

A. To store items, which are records

B. To run code functions

C. To manage user permissions

D. To host websites

Solution

1. Step 1: Understand the role of a table in DynamoDB

   A table is a container that holds items, which are like rows in a database.

2. Step 2: Identify the correct purpose

   Since tables store items (records), this matches To store items, which are records.

3. Final Answer:

   To store items, which are records -> Option A

4. Quick Check:

   Table = container for items [OK]

Hint: Tables hold records called items [OK]

Common Mistakes:

• Confusing tables with code functions
• Thinking tables manage permissions
• Assuming tables host websites

2. Which of the following is the correct way to define an item attribute in DynamoDB?

easy

A. ("Name", "John", "Age", 30)

B. {"Name": "John", "Age": 30}

C. ["Name", "John", "Age", 30]

D. "Name": "John", "Age": 30

Solution

1. Step 1: Recognize the attribute format

   Attributes are key-value pairs, best represented as JSON objects with keys and values.

2. Step 2: Match the correct syntax

   {"Name": "John", "Age": 30} shows a JSON object with keys "Name" and "Age" and their values, which is correct.

3. Final Answer:

   {"Name": "John", "Age": 30} -> Option B

4. Quick Check:

   Attributes = key-value pairs in JSON [OK]

Hint: Attributes are key-value pairs in JSON format [OK]

Common Mistakes:

• Using arrays instead of key-value pairs
• Using tuples instead of objects
• Omitting braces for JSON objects

3. Given a DynamoDB table with primary key "UserID", what happens if you try to add two items with the same UserID but different attributes?

medium

A. Both items are stored separately

B. The table creates a duplicate primary key

C. An error is thrown and no item is added

D. The second item overwrites the first item

Solution

1. Step 1: Understand primary key uniqueness

   In DynamoDB, the primary key must be unique for each item in the table.

2. Step 2: Effect of duplicate primary key

   If you add an item with an existing primary key, it replaces the old item with the new one.

3. Final Answer:

   The second item overwrites the first item -> Option D

4. Quick Check:

   Duplicate key = overwrite existing item [OK]

Hint: Duplicate primary keys overwrite existing items [OK]

Common Mistakes:

• Thinking both items are stored separately
• Expecting an error on duplicate keys
• Assuming duplicates are allowed

4. You try to insert an item into a DynamoDB table but get an error. The item has no primary key attribute. What is the most likely cause?

medium

A. Missing required primary key attribute in the item

B. Table is full and cannot accept new items

C. Attributes have invalid data types

D. You exceeded the maximum number of attributes

Solution

1. Step 1: Recall primary key requirement

   Every item must have the primary key attribute to be uniquely identified in the table.

2. Step 2: Identify cause of error

   If the item lacks the primary key attribute, DynamoDB rejects it with an error.

3. Final Answer:

   Missing required primary key attribute in the item -> Option A

4. Quick Check:

   Primary key missing causes insert error [OK]

Hint: Every item must include the primary key attribute [OK]

Common Mistakes:

• Assuming table capacity causes insert errors
• Blaming attribute data types without checking keys
• Thinking attribute count limits cause this error

5. You want to design a DynamoDB table to store user profiles. Each user has a unique UserID and may have multiple email addresses. How should you structure the table and items to handle this?

hard

A. Use email as the primary key and ignore UserID

B. Use UserID as the primary key and create a separate item for each email

C. Use UserID as the primary key and store emails as a list attribute inside each item

D. Create multiple tables, one per email address

Solution

1. Step 1: Identify unique identifier

   UserID uniquely identifies each user, so it should be the primary key.

2. Step 2: Store multiple emails

   Since a user can have multiple emails, store them as a list attribute inside the user item.

3. Step 3: Evaluate other options

   Creating separate items per email duplicates UserID or loses uniqueness; using email as key ignores UserID; multiple tables is inefficient.

4. Final Answer:

   Use UserID as the primary key and store emails as a list attribute inside each item -> Option C

5. Quick Check:

   Primary key + list attribute for multiple values [OK]

Hint: Use primary key for user, list attribute for multiple emails [OK]

Common Mistakes:

• Using email as primary key instead of UserID
• Creating multiple items for one user
• Making multiple tables unnecessarily