Return values on write in DynamoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What does ReturnValues: "ALL_OLD" return on a PutItem?

You perform a PutItem operation with ReturnValues set to "ALL_OLD". What will the response contain if the item did not exist before?

DynamoDB

PutItem({ TableName: "Users", Item: { UserId: "123", Name: "Alice" }, ReturnValues: "ALL_OLD" })

A The primary key attributes only

B An empty object because no previous item existed

C An error because <code>ALL_OLD</code> is invalid for <code>PutItem</code>

D The newly inserted item attributes

💡 Hint

Think about what ALL_OLD means when no item was replaced.

When ReturnValues is set to ALL_OLD in a PutItem, DynamoDB returns the old item attributes if the item existed. If the item did not exist, the response is empty.

❓ query_result

intermediate

What does ReturnValues: "UPDATED_NEW" return on an UpdateItem?

You run an UpdateItem with ReturnValues set to "UPDATED_NEW". What will the response contain?

DynamoDB

UpdateItem({ TableName: "Products", Key: { Id: "p1" }, UpdateExpression: "SET Price = :p", ExpressionAttributeValues: { ":p": 20 }, ReturnValues: "UPDATED_NEW" })

A All attributes of the item after the update

B All attributes of the item before the update

C Only the attributes that were updated with their new values

D No attributes, just a success status

💡 Hint

Focus on what UPDATED_NEW means in the context of updated attributes.

UPDATED_NEW returns only the attributes that were changed by the update, with their new values.

📝 Syntax

advanced

Which ReturnValues option is invalid for DeleteItem?

Select the ReturnValues option that will cause a syntax or runtime error when used with DeleteItem.

DynamoDB

DeleteItem({ TableName: "Orders", Key: { OrderId: "o123" }, ReturnValues: ? })

A "ALL_OLD"

B "ALL_NEW"

C "NONE"

D "UPDATED_NEW"

💡 Hint

Consider which return values make sense for a delete operation.

UPDATED_NEW is invalid for DeleteItem because no attributes are updated during deletion.

🧠 Conceptual

advanced

Why use ReturnValues: "ALL_NEW" in UpdateItem?

What is the main reason to set ReturnValues to "ALL_NEW" when updating an item?

A To get the entire item as it looks after the update

B To get only the attributes that were updated

C To get the item as it was before the update

D To prevent the update from happening if the item exists

💡 Hint

Think about when you want to see the full updated item.

ALL_NEW returns the entire item after the update, useful to confirm all changes.

🔧 Debug

expert

Why does this UpdateItem with ReturnValues: "ALL_OLD" return empty?

You run this UpdateItem on a non-existing item with ReturnValues set to "ALL_OLD". Why is the returned attribute map empty?

DynamoDB

UpdateItem({ TableName: "Inventory", Key: { ItemId: "i999" }, UpdateExpression: "SET Stock = :s", ExpressionAttributeValues: { ":s": 10 }, ReturnValues: "ALL_OLD" })

A Because the item did not exist before, so no old attributes to return

B Because <code>ALL_OLD</code> only returns updated attributes, and none were updated

C Because <code>ReturnValues</code> is ignored on <code>UpdateItem</code>

D Because the update failed silently without error

💡 Hint

Consider what ALL_OLD means when the item is new.

ALL_OLD returns the item attributes before the update. If the item did not exist, there are no old attributes to return, so the response is empty.

Practice

1. What does the ReturnValues parameter do in a DynamoDB write operation?

easy

A. It specifies what data should be returned after the write operation.

B. It controls the write capacity units consumed by the operation.

C. It sets the timeout duration for the write request.

D. It defines the table where data will be written.

Solution

1. Step 1: Understand the role of ReturnValues

   The ReturnValues parameter tells DynamoDB what data to send back after a write, such as old or new item attributes.

2. Step 2: Differentiate from other parameters

   ReturnValues does not affect capacity, timeout, or table selection; it only controls returned data.

3. Final Answer:

   It specifies what data should be returned after the write operation. -> Option A

4. Quick Check:

   ReturnValues controls returned data [OK]

Hint: ReturnValues returns data after write, not capacity or timeout [OK]

Common Mistakes:

• Confusing ReturnValues with capacity settings
• Thinking it sets request timeout
• Assuming it selects the table

2. Which of the following is the correct syntax to request the old item attributes after an update in DynamoDB using ReturnValues?

easy

A. "UPDATED_NEW"

B. "NONE"

C. "ALL_NEW"

D. "ALL_OLD"

Solution

1. Step 1: Recall ReturnValues options

   ReturnValues can be NONE, ALL_OLD, UPDATED_OLD, ALL_NEW, UPDATED_NEW.

2. Step 2: Identify option for old attributes after update

   "ALL_OLD" returns the entire item as it was before the update.

3. Final Answer:

   "ALL_OLD" -> Option D

4. Quick Check:

   Old attributes = ALL_OLD [OK]

Hint: Old data after update is ALL_OLD [OK]

Common Mistakes:

• Using ALL_NEW to get old data
• Confusing UPDATED_NEW with old data
• Setting NONE expecting data back

3. Given this DynamoDB update command snippet:

{
  TableName: "Users",
  Key: { "UserId": "123" },
  UpdateExpression: "SET Age = :newAge",
  ExpressionAttributeValues: { ":newAge": 30 },
  ReturnValues: "UPDATED_NEW"
}

What will the response contain?

medium

A. The entire item before the update.

B. Only the new Age attribute after the update.

C. No attributes, just success confirmation.

D. The entire item after the update.

Solution

1. Step 1: Understand ReturnValues "UPDATED_NEW" meaning

   This option returns only the attributes that were updated with their new values.

2. Step 2: Apply to given update

   The update changes Age to 30, so response includes only Age with value 30.

3. Final Answer:

   Only the new Age attribute after the update. -> Option B

4. Quick Check:

   UPDATED_NEW returns updated attributes [OK]

Hint: UPDATED_NEW returns only changed attributes with new values [OK]

Common Mistakes:

• Expecting full item back with UPDATED_NEW
• Confusing UPDATED_NEW with ALL_NEW
• Assuming no data returned with UPDATED_NEW

4. You wrote this DynamoDB PutItem request:

{
  TableName: "Products",
  Item: { "Id": "001", "Name": "Pen" },
  ReturnValues: "UPDATED_OLD"
}

But you get an error. What is wrong?

medium

A. ReturnValues must be set to "ALL_NEW" for PutItem.

B. The Item attribute is missing required keys.

C. "UPDATED_OLD" is invalid for PutItem operations.

D. TableName is incorrect.

Solution

1. Step 1: Check ReturnValues compatibility with PutItem

   PutItem supports only NONE or ALL_OLD for ReturnValues; UPDATED_OLD is invalid.

2. Step 2: Confirm other parameters

   Item and TableName are correct; error is due to invalid ReturnValues.

3. Final Answer:

   "UPDATED_OLD" is invalid for PutItem operations. -> Option C

4. Quick Check:

   PutItem supports NONE or ALL_OLD only [OK]

Hint: PutItem allows NONE or ALL_OLD only for ReturnValues [OK]

Common Mistakes:

• Using UPDATED_OLD with PutItem
• Assuming ALL_NEW required for PutItem
• Mistaking missing keys as cause

5. You want to update a user's email in DynamoDB and get back the entire updated item in one request. Which ReturnValues option should you use in your UpdateItem call?

hard

A. "ALL_NEW"

B. "UPDATED_OLD"

C. "NONE"

D. "ALL_OLD"

Solution

1. Step 1: Understand the goal

   You want the full updated item returned after the update.

2. Step 2: Match ReturnValues option

   "ALL_NEW" returns the entire item as it looks after the update.

3. Final Answer:

   "ALL_NEW" -> Option A

4. Quick Check:

   Full updated item = ALL_NEW [OK]

Hint: Use ALL_NEW to get full updated item after update [OK]

Common Mistakes:

• Choosing UPDATED_OLD which returns old updated attributes
• Using NONE expecting data back
• Selecting ALL_OLD which returns old full item