Attribute types (S, N, B, BOOL, L, M) in DynamoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this DynamoDB item retrieval?

Given a DynamoDB item with attribute types:

{"Name": {"S": "Alice"}, "Age": {"N": "30"}, "Active": {"BOOL": true}}

What will be the value of the "Age" attribute when retrieved?

A 30 (number)

B "30" (string)

C true (boolean)

D null (no value)

💡 Hint

Remember that DynamoDB stores numbers as strings in the N type.

DynamoDB stores numbers as strings under the N attribute type internally, but when retrieved via the AWS SDK, the value is returned as a numeric type. So when you retrieve the Age attribute, its value is the number 30, not a string.

❓ query_result

intermediate

What is the output of this DynamoDB item with nested map and list?

Consider this DynamoDB item:

{"User": {"M": {"Name": {"S": "Bob"}, "Scores": {"L": [{"N": "10"}, {"N": "20"}]}}}}

What is the value type of "Scores" inside "User"?

A Map of numbers

B List of numbers

C List of strings

D Map of strings

💡 Hint

Look at the L and N attribute types inside the Scores attribute.

The Scores attribute is a list (L) containing two numbers (N). So it is a list of numbers.

📝 Syntax

advanced

Which option correctly defines a DynamoDB item with a binary attribute?

You want to store a binary attribute named "ImageData" in DynamoDB. Which of the following JSON representations is syntactically correct?

A {"ImageData": {"B": "aGVsbG8="}}

B {"ImageData": {"N": "aGVsbG8="}}

C {"ImageData": {"S": "aGVsbG8="}}

D {"ImageData": {"BOOL": "aGVsbG8="}}

💡 Hint

Binary data uses the B attribute type and is base64 encoded.

The B attribute type is used for binary data and expects a base64 encoded string. Option A correctly uses B with a base64 string.

🧠 Conceptual

advanced

Which attribute type is best to store a true/false value in DynamoDB?

You want to store a flag indicating if a user is active or not. Which DynamoDB attribute type should you use?

A S (String)

B N (Number)

C B (Binary)

D BOOL (Boolean)

💡 Hint

DynamoDB has a dedicated type for true/false values.

The BOOL attribute type is designed to store boolean true or false values directly.

🔧 Debug

expert

Why does this DynamoDB query fail to retrieve the nested map attribute?

You have this item:

{"Profile": {"M": {"Name": {"S": "Eve"}, "Count": {"M": {"Age": {"N": "25"}}}}}}

You try to get the Age value with this expression:

ProjectionExpression: "Profile.Count.Age"

But the query returns no value for Age. What is the likely cause?

A DynamoDB does not support nested map attributes

B Age attribute is missing from the item

C ProjectionExpression syntax requires using # placeholders for nested map keys

D ProjectionExpression must use dot notation only for list attributes

💡 Hint

Check how DynamoDB handles nested attribute names in ProjectionExpression.

DynamoDB requires using expression attribute names (like #P, #C, #A) to access nested map keys in ProjectionExpression to avoid reserved word conflicts.

Practice

1.

Which DynamoDB attribute type is used to store plain text strings?

easy

A. B

B. N

C. BOOL

D. S

Solution

1. Step 1: Understand attribute types in DynamoDB

   DynamoDB uses attribute types to define data kinds. 'S' stands for string (text).

2. Step 2: Match the type to text data

   Since 'S' means string, it is the correct type for plain text.

3. Final Answer:

   S -> Option D

4. Quick Check:

   Text data = S [OK]

Hint: Text data always uses type S in DynamoDB [OK]

Common Mistakes:

• Confusing N (number) with S (string)
• Choosing BOOL for text
• Using B for text data

2.

Which of the following is the correct syntax to define a boolean attribute named isActive in a DynamoDB item?

{"isActive": {"BOOL": true}}

easy

A. {"isActive": {"S": "true"}}

B. {"isActive": {"BOOL": true}}

C. {"isActive": {"N": 1}}

D. {"isActive": {"B": true}}

Solution

1. Step 1: Identify the correct attribute type for boolean

   Boolean values in DynamoDB use the BOOL type with true or false.

2. Step 2: Check the syntax for boolean attribute

   The correct syntax is {"isActive": {"BOOL": true}} to represent a boolean true.

3. Final Answer:

   {"isActive": {"BOOL": true}} -> Option B

4. Quick Check:

   Boolean attribute uses BOOL type [OK]

Hint: Use BOOL type with true/false for boolean values [OK]

Common Mistakes:

• Using S type with string 'true'
• Using N type with 1 instead of BOOL
• Using B type for boolean

3.

Given the following DynamoDB item attribute, what is the type of tags?

{"tags": {"L": [ {"S": "red"}, {"S": "blue"}, {"S": "green"} ] }}

medium

A. List (L)

B. Map (M)

C. String (S)

D. Binary (B)

Solution

1. Step 1: Identify the attribute type key

   The attribute uses the key "L", which stands for List in DynamoDB.

2. Step 2: Understand the value structure

   The value is an array of strings, confirming it is a list of string elements.

3. Final Answer:

   List (L) -> Option A

4. Quick Check:

   Attribute key L means List [OK]

Hint: Look for L key to identify lists in DynamoDB [OK]

Common Mistakes:

• Confusing L with M (map)
• Thinking it's a string because of S inside list
• Choosing B for binary data

4.

Identify the error in this DynamoDB attribute definition:

{"profile": {"M": {"age": {"S": 30}, "name": {"S": "Alice"}}}}

medium

A. The name attribute should use type N, not S

B. The map (M) type cannot contain nested attributes

C. The age attribute should use type N, not S

D. Binary (B) type is missing for profile

Solution

1. Step 1: Analyze the attribute types inside the map

   The map contains "age" with type S and value 30, and "name" with type S and value "Alice".

2. Step 2: Check if types match values

   Age is a number (30), so it should use type N, not S (string). Name is correctly a string.

3. Final Answer:

   Age attribute should use type N, not S -> Option C

4. Quick Check:

   Numbers use N type, not S [OK]

Hint: Numbers inside maps must use N type, not S [OK]

Common Mistakes:

• Using S for numbers
• Thinking maps can't nest attributes
• Confusing name type as number

5.

You want to store a user's profile with a list of phone numbers and a map of address details in DynamoDB. Which attribute types should you use for phoneNumbers and address respectively?

hard

A. phoneNumbers: L, address: M

B. phoneNumbers: M, address: L

C. phoneNumbers: S, address: B

D. phoneNumbers: BOOL, address: N

Solution

1. Step 1: Identify the type for a list of phone numbers

   A list of phone numbers is a collection, so it should use the List (L) type.

2. Step 2: Identify the type for address details as key-value pairs

   Address details are structured data with keys and values, so Map (M) type is appropriate.

3. Final Answer:

   phoneNumbers: L, address: M -> Option A

4. Quick Check:

   Lists = L, Maps = M [OK]

Hint: Use L for lists, M for maps (objects) in DynamoDB [OK]

Common Mistakes:

• Swapping L and M types
• Using S for lists
• Using BOOL or N incorrectly