Return values on write in DynamoDB - Mini Project: Build & Apply

Return Values on Write in DynamoDB

📖 Scenario: You are managing a simple inventory system using DynamoDB. You want to add new items and update existing items while seeing what changes were made after each write operation.

🎯 Goal: Build a DynamoDB table and perform write operations that return the previous or updated item attributes using the ReturnValues parameter.

📋 What You'll Learn

Create a DynamoDB table named Inventory with ItemId as the primary key.

Insert an item with specific attributes.

Update an item and use ReturnValues to get the old attributes.

Use ReturnValues to get the updated attributes after a write.

💡 Why This Matters

🌍 Real World

In real DynamoDB usage, ReturnValues helps you see what changed after an update or delete without making a separate read call.

💼 Career

Understanding ReturnValues is important for backend developers and database administrators working with AWS DynamoDB to optimize data operations and reduce extra reads.

1

Create the Inventory table and add an initial item

Create a dictionary called inventory_table representing the DynamoDB table with a key ItemId and add an item with ItemId set to "1001", Name set to "Notebook", and Quantity set to 50.

DynamoDB

# Create the inventory_table dictionary with one item
# Your code here

Hint

Use a dictionary where the key is the ItemId and the value is another dictionary with Name and Quantity.

2

Set the ReturnValues configuration for update

Create a variable called return_values and set it to the string "ALL_OLD" to specify that the update operation should return the old attributes of the item.

DynamoDB

inventory_table = {
    "1001": {"Name": "Notebook", "Quantity": 50}
}
# Set return_values to "ALL_OLD"
# Your code here

Hint

The ReturnValues parameter controls what the update operation returns. Use "ALL_OLD" to get the previous item attributes.

3

Update the item and get old attributes

Write a function called update_quantity that takes item_id, new_quantity, and return_values as parameters. Inside the function, update the Quantity of the item in inventory_table with item_id to new_quantity and return the old attributes if return_values is "ALL_OLD". Use the variable names exactly as specified.

DynamoDB

inventory_table = {
    "1001": {"Name": "Notebook", "Quantity": 50}
}
return_values = "ALL_OLD"

# Define update_quantity function
# Your code here

Hint

Copy the old attributes before updating. Return them if return_values is "ALL_OLD".

4

Use ReturnValues to get updated attributes after write

Add a variable called return_values_updated and set it to "ALL_NEW". Then write a function called update_name that takes item_id, new_name, and return_values as parameters. Inside the function, update the Name of the item in inventory_table with item_id to new_name and return the updated attributes if return_values is "ALL_NEW". Use the variable and function names exactly as specified.

DynamoDB

inventory_table = {
    "1001": {"Name": "Notebook", "Quantity": 50}
}
return_values = "ALL_OLD"

def update_quantity(item_id, new_quantity, return_values):
    old_attributes = inventory_table[item_id].copy()
    inventory_table[item_id]["Quantity"] = new_quantity
    if return_values == "ALL_OLD":
        return old_attributes
    return None

# Set return_values_updated to "ALL_NEW" and define update_name function
# Your code here

Hint

Return the updated item attributes if return_values is "ALL_NEW".

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