Expression attribute names in DynamoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Using Expression Attribute Names to Access Reserved Words

You have a DynamoDB table with an attribute named "Name", which is a reserved word. You want to update the attribute "Name" to "Alice" for the item with "ID" = 123.

Which update expression and expression attribute names will correctly update the item?

DynamoDB

UpdateExpression = "SET #N = :val"
ExpressionAttributeNames = {"#N": "Name"}
ExpressionAttributeValues = {":val": "Alice"}

A UpdateExpression = "SET Name = :val" without ExpressionAttributeNames

B UpdateExpression = "SET #N = :val" with ExpressionAttributeNames = {"#N": "Name"}

C UpdateExpression = "SET #Name = :val" with ExpressionAttributeNames = {"#Name": "Name"}

D UpdateExpression = "SET #N = :val" with ExpressionAttributeNames = {"#Name": "Name"}

💡 Hint

Reserved words require you to use expression attribute names with a placeholder starting with #.

Because "Name" is a reserved word, you must use an expression attribute name placeholder like #N mapped to "Name". Option B correctly uses #N and maps it properly.

📝 Syntax

intermediate

Identify the Syntax Error in Expression Attribute Names Usage

Which option contains a syntax error in the use of expression attribute names in a DynamoDB update expression?

DynamoDB

UpdateExpression = "SET #A = :val"
ExpressionAttributeNames = {"#A": "Age"}
ExpressionAttributeValues = {":val": 30}

A ExpressionAttributeNames = {"A": "Age"}

B ExpressionAttributeNames = {"#A": "#Age"}

C ExpressionAttributeNames = {"#A": "Age"}

D ExpressionAttributeNames = {"#Age": "Age"}

💡 Hint

Expression attribute names must start with a # symbol in the key.

Option A is missing the # prefix in the key of ExpressionAttributeNames, which causes a syntax error.

❓ query_result

advanced

Effect of Incorrect Expression Attribute Names Mapping

You run the following DynamoDB update command:

UpdateExpression = "SET #A = :val"
ExpressionAttributeNames = {"#B": "Age"}
ExpressionAttributeValues = {":val": 25}

What will happen when this command is executed?

A A runtime error occurs because #A is not defined in ExpressionAttributeNames

B The attribute "Age" will be updated to 25

C The attribute "#A" will be created and set to 25

D The update will succeed but no attribute will be changed

💡 Hint

Check if all placeholders in UpdateExpression are defined in ExpressionAttributeNames.

The UpdateExpression uses #A but ExpressionAttributeNames defines #B. This mismatch causes a runtime error.

❓ optimization

advanced

Optimizing Expression Attribute Names for Multiple Reserved Words

You want to update two reserved word attributes, "Status" and "Order", in a DynamoDB item. Which option uses expression attribute names most efficiently?

A

ExpressionAttributeNames = {"Status": "Status", "Order": "Order"}
UpdateExpression = "SET Status = :s, Order = :o"

B

ExpressionAttributeNames = {"#Status": "Status", "#Order": "Order"}
UpdateExpression = "SET #Status = :s, #Order = :o"

C

ExpressionAttributeNames = {"#S": "Status", "#S": "Order"}
UpdateExpression = "SET #S = :s, #S = :o"

D

ExpressionAttributeNames = {"#S": "Status", "#O": "Order"}
UpdateExpression = "SET #S = :s, #O = :o"

💡 Hint

Each placeholder must be unique and map to one attribute name.

Option D correctly uses unique placeholders #S and #O for the reserved words. Option D repeats the same placeholder key, which is invalid. Option D does not use placeholders for reserved words. Option D uses longer placeholders but is less concise.

🔧 Debug

expert

Debugging a Complex UpdateExpression with Nested Attributes

You want to update a nested attribute "info.Name" in a DynamoDB item. The attribute "Name" is reserved. You write:

UpdateExpression = "SET #info.#N = :val"
ExpressionAttributeNames = {"#info": "info", "#N": "Name"}
ExpressionAttributeValues = {":val": "Bob"}

What will be the result of this update?

A The attribute #info.#N will be created literally as a string key

B A syntax error occurs due to incorrect use of expression attribute names for nested attributes

C The nested attribute info.Name will be updated to "Bob" successfully

D A runtime error occurs because nested attribute placeholders are not supported

💡 Hint

Expression attribute names can be used for nested attributes by prefixing each part.

Option C is correct because each part of the nested attribute path uses a placeholder, which is the correct way to handle reserved words in nested attributes.