Put, get, and query operations in AWS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does a Put operation do in AWS DynamoDB?

A Put operation adds a new item or replaces an existing item in a DynamoDB table. Think of it like putting a new book on a shelf or replacing an old one with a new copy.

beginner

What is the purpose of a Get operation in AWS DynamoDB?

A Get operation retrieves a single item from a DynamoDB table using its primary key. It's like looking up a specific book by its unique ID on a shelf.

intermediate

How does a Query operation differ from a Get operation in DynamoDB?

A Query operation finds multiple items based on a partition key and optional filters. Unlike Get, which fetches one item, Query can return many items that share the same partition key, like finding all books by the same author.

intermediate

Why should you use Query instead of Scan in DynamoDB when possible?

Query is faster and more efficient because it looks only at items with a specific partition key. Scan checks every item in the table, which is slower and uses more resources, like searching every book in a library instead of just one shelf.

beginner

What happens if you Put an item with the same primary key as an existing item in DynamoDB?

The existing item is replaced with the new one. It's like swapping an old book with a new edition on the same shelf spot.

Which DynamoDB operation retrieves a single item by its primary key?

A Query

B Put

C Get

D Scan

Get operation fetches one item using its primary key.

What does a Put operation do if the item key already exists?

A Returns an error

B Deletes the old item

C Adds a duplicate item

D Replaces the existing item

Put replaces the existing item with the new one if the key matches.

Which operation is best to find all items with the same partition key?

A Query

B Put

C Get

D Scan

Query returns multiple items sharing the same partition key.

Why is Query preferred over Scan in DynamoDB?

A Query is slower but more thorough

B Query only looks at relevant items, making it faster

C Scan uses less resources

D Scan returns fewer items

Query is faster because it targets specific partition keys.

Which operation would you use to add a new item to a DynamoDB table?

A Put

B Scan

C Query

D Get

Put operation adds or replaces an item in the table.

Explain the differences between Put, Get, and Query operations in DynamoDB.

Think about how you add, find one, or find many books in a library.

Describe why Query is more efficient than Scan in DynamoDB and when you should use each.

Compare searching one shelf versus the whole library.

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