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.