Attribute types (S, N, B, BOOL, L, M) in DynamoDB

Introduction

Attribute types tell DynamoDB what kind of data you are storing. This helps DynamoDB organize and find your data easily.

When you want to store text like names or descriptions.

When you need to save numbers like prices or ages.

When you want to keep binary data like images or files.

When you want to store true or false values.

When you want to save a list of items.

When you want to store a group of key-value pairs (like a small object).

Syntax

DynamoDB

AttributeName: { S: "string" }
AttributeName: { N: "number_as_string" }
AttributeName: { B: binary_data }
AttributeName: { BOOL: true_or_false }
AttributeName: { L: [list_of_attributes] }
AttributeName: { M: { map_of_attributes } }

S means String, N means Number, B means Binary, BOOL means Boolean (true/false), L means List, and M means Map (like an object).

Numbers are stored as strings to keep precision.

Examples

This stores a text value "Alice" in the attribute Name.

DynamoDB

Name: { S: "Alice" }

This stores the number 30 in the attribute Age.

DynamoDB

Age: { N: "30" }

This stores a true/false value indicating if something is active.

DynamoDB

IsActive: { BOOL: true }

This stores a list of strings "red" and "blue" in the attribute Tags.

DynamoDB

Tags: { L: [ { S: "red" }, { S: "blue" } ] }

This stores a map (like an object) with City and Zip inside Address.

DynamoDB

Address: { M: { City: { S: "NY" }, Zip: { N: "10001" } } }

Sample Program

This example shows a full item with different attribute types: string, number, boolean, list, and map.

DynamoDB

PUT Item {
  "UserId": { S: "user123" },
  "Age": { N: "25" },
  "IsMember": { BOOL: true },
  "Favorites": { L: [ { S: "chocolate" }, { S: "vanilla" } ] },
  "Profile": { M: { "Height": { N: "170" }, "Weight": { N: "65" } } }
}

Important Notes

Always wrap numbers as strings in the N type to avoid errors.

Lists (L) can hold mixed attribute types, like strings and numbers together.

Maps (M) let you nest attributes inside one another, like a small object.

Summary

Attribute types tell DynamoDB what kind of data you store.

S is for text, N is for numbers, B is for binary data, BOOL is for true/false.

L is for lists, and M is for maps (objects).

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