Why CRUD operations are foundational in DynamoDB - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new item in a DynamoDB table.

DynamoDB

response = table.[1](Item={'UserId': '123', 'Name': 'Alice'})

Drag options to blanks, or click blank then click option'

Aput_item

Bget_item

Cdelete_item

Dupdate_item

Attempts:

3 left

💡 Hint

Common Mistakes

Using get_item instead of put_item

Using update_item without an existing item

The put_item method adds a new item to the table.

2fill in blank

medium

Complete the code to read an item from a DynamoDB table by its key.

DynamoDB

response = table.[1](Key={'UserId': '123'})

Drag options to blanks, or click blank then click option'

Aput_item

Bget_item

Cdelete_item

Dupdate_item

Attempts:

3 left

💡 Hint

Common Mistakes

Using put_item to read data

Using delete_item instead of get_item

The get_item method retrieves an item by its key.

3fill in blank

hard

Fix the error in the code to update an existing item in DynamoDB.

DynamoDB

response = table.[1](Key={'UserId': '123'}, UpdateExpression='SET Age = :age', ExpressionAttributeValues={':age': 30})

Drag options to blanks, or click blank then click option'

Aget_item

Bput_item

Cupdate_item

Ddelete_item

Attempts:

3 left

💡 Hint

Common Mistakes

Using put_item which replaces the whole item

Using get_item which only reads data

The update_item method updates attributes of an existing item.

4fill in blank

hard

Fill both blanks to delete an item by key and confirm the operation.

DynamoDB

response = table.[1](Key=[2])

Drag options to blanks, or click blank then click option'

Adelete_item

B{'UserId': '123'}

C{'Name': 'Alice'}

Dput_item

Attempts:

3 left

💡 Hint

Common Mistakes

Using put_item instead of delete_item

Providing wrong key structure

delete_item removes the item with the specified key from the table.

5fill in blank

hard

Fill all three blanks to create an item and then read it back.

DynamoDB

table.[1](Item={'UserId': '456', 'Name': 'Bob'})
response = table.[2](Key=[3])

Drag options to blanks, or click blank then click option'

Aput_item

Bget_item

C{'UserId': '456'}

Ddelete_item

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up method names

Using wrong key format

This sequence creates an item, reads it back, and the key is used to identify the item.

Practice

1. What does the CRUD acronym stand for in database operations?

easy

A. Calculate, Remove, Upload, Download

B. Create, Read, Update, Delete

C. Copy, Run, Undo, Drop

D. Connect, Retrieve, Use, Delete

Solution

1. Step 1: Understand each letter in CRUD

   CRUD stands for the four basic operations to manage data: Create, Read, Update, and Delete.

2. Step 2: Match the correct full form

   Among the options, only Create, Read, Update, Delete correctly lists these four operations.

3. Final Answer:

   Create, Read, Update, Delete -> Option B

4. Quick Check:

   CRUD = Create, Read, Update, Delete [OK]

Hint: Remember CRUD as the four main data actions [OK]

Common Mistakes:

• Confusing CRUD with unrelated terms
• Mixing up the order of operations
• Thinking CRUD includes 'Copy' or 'Calculate'

2. Which of the following is the correct syntax to add a new item in DynamoDB using the AWS SDK?

easy

A. dynamodb.putItem({ TableName: 'Users', Item: { 'UserId': { S: '123' } } })

B. dynamodb.getItem({ TableName: 'Users', Key: { 'UserId': { S: '123' } } })

C. dynamodb.deleteItem({ TableName: 'Users', Key: { 'UserId': { S: '123' } } })

D. dynamodb.updateItem({ TableName: 'Users', Key: { 'UserId': { S: '123' } } })

Solution

1. Step 1: Identify the operation to add a new item

   Adding a new item uses the putItem method in DynamoDB.

2. Step 2: Match the correct syntax

   dynamodb.putItem({ TableName: 'Users', Item: { 'UserId': { S: '123' } } }) uses putItem with the correct parameters to add an item.

3. Final Answer:

   dynamodb.putItem({ TableName: 'Users', Item: { 'UserId': { S: '123' } } }) -> Option A

4. Quick Check:

   Adding item = putItem [OK]

Hint: Use putItem to create new data in DynamoDB [OK]

Common Mistakes:

• Using getItem or deleteItem to add data
• Confusing Key with Item in parameters
• Missing TableName or Item fields

3. Given the following DynamoDB operation, what will be the result?

const params = { TableName: 'Books', Key: { 'ISBN': { S: '978-1234567890' } } };
const data = await dynamodb.getItem(params).promise();
console.log(data.Item);

medium

A. It will cause a syntax error

B. It will delete the item with ISBN '978-1234567890'

C. It will update the item with ISBN '978-1234567890'

D. It will print the item with ISBN '978-1234567890' if it exists

Solution

1. Step 1: Understand the getItem operation

   The getItem method retrieves an item by its key from the table.

2. Step 2: Analyze the code output

   The code logs data.Item, which will be the item with the given ISBN if it exists, or undefined if not.

3. Final Answer:

   It will print the item with ISBN '978-1234567890' if it exists -> Option D

4. Quick Check:

   getItem returns item data [OK]

Hint: getItem fetches data; console.log prints it [OK]

Common Mistakes:

• Thinking getItem deletes or updates data
• Assuming syntax error due to async/await
• Confusing Key with Item in parameters

4. You wrote this DynamoDB update code but it throws an error:

const params = {
  TableName: 'Users',
  Key: { 'UserId': { S: 'abc123' } },
  UpdateExpression: 'set Age = :age',
  ExpressionAttributeValues: { ':age': 30 }
};
await dynamodb.updateItem(params).promise();

What is the likely cause of the error?

medium

A. ExpressionAttributeValues must use DynamoDB types like { ':age': { N: '30' } }

B. UpdateExpression should be 'update Age = :age'

C. Key should be inside Item property

D. TableName is missing

Solution

1. Step 1: Check ExpressionAttributeValues format

   DynamoDB expects attribute values to be typed, e.g., numbers as { N: '30' }.

2. Step 2: Identify the error cause

   The code uses a plain number 30 instead of the typed format, causing a validation error.

3. Final Answer:

   ExpressionAttributeValues must use DynamoDB types like { ':age': { N: '30' } } -> Option A

4. Quick Check:

   Use typed values in ExpressionAttributeValues [OK]

Hint: Always wrap values with DynamoDB types in updates [OK]

Common Mistakes:

• Using raw JS values instead of typed DynamoDB values
• Wrong UpdateExpression syntax
• Misplacing Key inside Item

5. You want to delete a user from a DynamoDB table only if their account is inactive. Which approach correctly combines CRUD operations to achieve this safely?

hard

A. Use putItem to overwrite the user with an empty item

B. Use updateItem to set AccountStatus to 'deleted' without conditions

C. Use deleteItem with a ConditionExpression checking if AccountStatus = 'inactive'

D. Use getItem to read then deleteItem without conditions

Solution

1. Step 1: Understand safe deletion with conditions

   To delete only if a condition is met, use deleteItem with a ConditionExpression.

2. Step 2: Evaluate options for correctness

   Use deleteItem with a ConditionExpression checking if AccountStatus = 'inactive' uses deleteItem with a condition to delete only inactive accounts, which is safe and efficient.

3. Final Answer:

   Use deleteItem with a ConditionExpression checking if AccountStatus = 'inactive' -> Option C

4. Quick Check:

   Conditional delete = deleteItem + ConditionExpression [OK]

Hint: Use ConditionExpression to safely delete items [OK]

Common Mistakes:

• Deleting without checking account status
• Using updateItem to delete data
• Overwriting with putItem instead of deleting