Put, get, and query operations in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

DynamoDB PutItem operation behavior

You use the AWS DynamoDB PutItem operation to add an item with a primary key that already exists in the table. What happens to the existing item?

A The new item is merged with the existing item, updating only specified attributes.

B The PutItem operation fails with a ConditionalCheckFailedException.

C The existing item is replaced with the new item completely.

D The PutItem operation appends the new item as a duplicate entry.

💡 Hint

Think about how PutItem treats items with the same primary key.

PutItem replaces the entire existing item if the primary key matches. It does not merge or append duplicates.

❓ service_behavior

intermediate

DynamoDB GetItem consistency options

When you perform a GetItem operation in DynamoDB, which option ensures you get the most up-to-date data?

A Set the ConsistentRead parameter to true for a strongly consistent read.

B Use the default eventually consistent read option.

C Use a Query operation instead of GetItem.

D Enable DynamoDB Streams to get the latest data.

💡 Hint

Consider how DynamoDB handles read consistency.

Setting ConsistentRead to true in GetItem returns strongly consistent data, ensuring the latest updates are read.

❓ Configuration

advanced

DynamoDB Query operation with filter expression

You want to retrieve all items from a DynamoDB table where the partition key is 'User123' and the attribute 'Status' equals 'Active'. Which Query operation parameters correctly achieve this?

AWS

TableName: 'Users'
KeyConditionExpression: 'UserId = :uid'
FilterExpression: 'Status = :status'
ExpressionAttributeValues: { ':uid': {S: 'User123'}, ':status': {S: 'Active'} }

A Use only FilterExpression for both UserId and Status.

B Use KeyConditionExpression for both UserId and Status attributes.

C Use FilterExpression for UserId and KeyConditionExpression for Status.

D Use KeyConditionExpression for UserId and FilterExpression for Status.

💡 Hint

Remember that KeyConditionExpression must include the partition key.

KeyConditionExpression filters by partition key and optionally sort key. FilterExpression filters non-key attributes after the query.

❓ Architecture

advanced

Efficient retrieval of multiple items by keys

You need to retrieve multiple items from a DynamoDB table by their primary keys in a single request. Which operation is the most efficient and appropriate?

A Use multiple GetItem requests in parallel.

B Use BatchGetItem operation with all keys specified.

C Use Query operation with multiple KeyConditionExpressions.

D Use Scan operation with a filter on primary keys.

💡 Hint

Consider which operation supports multiple keys in one call.

BatchGetItem allows retrieving multiple items by primary keys in a single request efficiently.

❓ security

expert

Securing DynamoDB PutItem operations with IAM policies

You want to restrict an IAM user so they can only perform PutItem operations on a DynamoDB table but only for items where the attribute 'Department' equals 'Sales'. Which IAM policy condition correctly enforces this?

A "Condition": {"StringEquals": {"dynamodb:Attributes/Department": "Sales"}}

B "Condition": {"ForAllValues:StringEquals": {"dynamodb:Attributes/Department": "Sales"}}

C "Condition": {"StringEqualsIfExists": {"dynamodb:LeadingKeys": ["Sales"]}}

D "Condition": {"StringEquals": {"dynamodb:LeadingKeys": ["Sales"]}}

💡 Hint

Think about how to restrict based on an attribute value in IAM conditions.

The condition "StringEquals" on "dynamodb:Attributes/Department" restricts PutItem to items where Department equals 'Sales'.

Practice

1. What does the put operation do in AWS DynamoDB?

easy

A. Saves or updates an item in the table

B. Retrieves a single item by its key

C. Searches items based on key conditions

D. Deletes an item from the table

Solution

1. Step 1: Understand the purpose of put

   The put operation is used to save a new item or update an existing item in a DynamoDB table.

2. Step 2: Compare with other operations

   get retrieves one item by key, query searches by key conditions, and delete removes an item.

3. Final Answer:

   Saves or updates an item in the table -> Option A

4. Quick Check:

   Put = Save or update [OK]

Hint: Put means save or update data [OK]

Common Mistakes:

• Confusing put with get or query
• Thinking put deletes data
• Assuming put only adds new items

2. Which of the following is the correct syntax to get an item by its key in AWS SDK for JavaScript DynamoDB client?

easy

A. dynamoDBClient.put({ TableName: 'MyTable', Item: { id: '123' } })

B. dynamoDBClient.get({ TableName: 'MyTable', Key: { id: '123' } })

C. dynamoDBClient.query({ TableName: 'MyTable', KeyConditionExpression: 'id = :id' })

D. dynamoDBClient.getItem({ TableName: 'MyTable', Key: { id: '123' } })

Solution

1. Step 1: Identify the correct method for getting an item

   The AWS SDK for JavaScript v3 uses get method on the DynamoDB DocumentClient to retrieve a single item by key.

2. Step 2: Check the parameters

   The parameters include TableName and Key with the key attribute and value.

3. Final Answer:

   dynamoDBClient.get({ TableName: 'MyTable', Key: { id: '123' } }) -> Option B

4. Quick Check:

   Get item uses get() with TableName and Key [OK]

Hint: Get single item uses get() with Key [OK]

Common Mistakes:

• Using getItem() instead of get()
• Confusing query with get
• Using put() to get data

3. Given this DynamoDB query code snippet, what will be the output if the table contains items with userId 'user1' and 'user2' only?

const params = {
  TableName: 'Users',
  KeyConditionExpression: 'userId = :uid',
  ExpressionAttributeValues: { ':uid': 'user1' }
};
const result = await dynamoDBClient.query(params);
console.log(result.Items);

medium

A. [{ userId: 'user2', name: 'Bob' }]

B. []

C. [{ userId: 'user1', name: 'Alice' }]

D. Error: Missing Key

Solution

1. Step 1: Understand the query parameters

   The query searches for items where userId equals 'user1'.

2. Step 2: Match items in the table

   Since the table has 'user1' and 'user2', only the item with 'user1' matches and is returned.

3. Final Answer:

   [{ userId: 'user1', name: 'Alice' }] -> Option C

4. Quick Check:

   Query filters by key condition, returns matching items [OK]

Hint: Query returns items matching key condition [OK]

Common Mistakes:

• Expecting all items returned
• Confusing query with scan
• Thinking query returns error without full key

4. You wrote this code to get an item but it throws an error:

const params = {
  TableName: 'Products',
  Key: { productId: 101 }
};
const data = await dynamoDBClient.getItem(params);
console.log(data.Item);

What is the likely cause of the error?

medium

A. The key attribute value must be a string, not a number

B. The method should be get instead of getItem

C. Missing KeyConditionExpression in parameters

D. TableName is incorrect

Solution

1. Step 1: Check the key attribute type

   DynamoDB keys must be typed as attribute values, usually strings or objects with type wrappers.

2. Step 2: Identify the error cause

   Passing a plain number (101) without type wrapper causes a validation error.

3. Final Answer:

   The key attribute value must be a string, not a number -> Option A

4. Quick Check:

   Key values need correct type format [OK]

Hint: Key values must be strings or typed attributes [OK]

Common Mistakes:

• Using wrong method name
• Missing KeyConditionExpression in getItem
• Incorrect table name

5. You want to update a user's email in DynamoDB only if the user exists. Which operation and condition should you use?

hard

A. Use query to find the user, then put to update

B. Use get to check existence, then put to update

C. Use put without any condition

D. Use put with a condition expression checking attribute_exists(userId)

Solution

1. Step 1: Understand conditional update

   To update only if the user exists, use put with a condition expression that checks for the user's existence.

2. Step 2: Use attribute_exists condition

   The condition attribute_exists(userId) ensures the item exists before updating, preventing overwriting non-existing items.

3. Final Answer:

   Use put with a condition expression checking attribute_exists(userId) -> Option D

4. Quick Check:

   Conditional put prevents overwriting missing items [OK]

Hint: Use put with condition attribute_exists() to update safely [OK]

Common Mistakes:

• Using get then put causes race conditions
• Using query unnecessarily for single item
• Putting without condition overwrites blindly