Put, get, and query operations in AWS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to put an item into a DynamoDB table.

AWS

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

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

Aquery

Bput_item

Cget_item

Dscan

Attempts:

3 left

💡 Hint

Common Mistakes

Using get_item instead of put_item will try to retrieve data, not add it.

Using query or scan are for reading data, not writing.

The put_item method adds a new item to the DynamoDB table.

2fill in blank

medium

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

AWS

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

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

Aquery

Bput_item

Cget_item

Ddelete_item

Attempts:

3 left

💡 Hint

Common Mistakes

Using put_item will add data instead of retrieving it.

Using query is for searching with conditions, not direct key retrieval.

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

3fill in blank

hard

Fix the error in the query operation to find items with UserId '123'.

AWS

response = table.query(
    KeyConditionExpression=Key('UserId').[1]('123')
)

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

Aeq

Bequals

Cequal

Dmatch

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'equals' or 'equal' causes errors because they are not valid methods.

Using 'match' is not a DynamoDB Key method.

The eq method is used in KeyConditionExpression to specify equality in DynamoDB queries.

4fill in blank

hard

Fill both blanks to query items where UserId equals '123' and Status equals 'active'.

AWS

response = table.query(
    KeyConditionExpression=Key('UserId').[1]('123') & Key('Status').[2]('active')
)

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

Aeq

Bgt

Dlt

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'gt' or 'lt' will filter for greater or less than, not equality.

Mixing different methods causes query errors.

Both conditions use eq to check for equality in the query.

5fill in blank

hard

Fill all three blanks to get items with UserId '123', Status 'active', and sort by Timestamp descending.

AWS

response = table.query(
    KeyConditionExpression=Key('UserId').[1]('123') & Key('Status').[2]('active'),
    ScanIndexForward=[3]
)

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

Aeq

CFalse

DTrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using True for ScanIndexForward sorts ascending, not descending.

Using other methods than 'eq' for conditions causes errors.

The query filters by equality on UserId and Status, and sets ScanIndexForward=False to sort results in descending order.

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