Put, get, and query operations in AWS - Step-by-Step Execution

Process Flow - Put, get, and query operations

Start Operation

↓

Choose Operation Type

↓

Write

↓

Data

↓

Confirm

↓

Success

↓

End

This flow shows how AWS data operations start by choosing Put, Get, or Query, then perform writing, reading by key, or searching by condition, and finally return success or data.

Execution Sample

AWS

PutItem: Add item with key=123
GetItem: Retrieve item with key=123
Query: Find items where status='active'

This code shows adding an item, retrieving it by key, and searching items by a condition.

Process Table

Step	Operation	Input	Action	Output
1	PutItem	Item {id:123, name:'Book'}	Write item to table	Success confirmation
2	GetItem	Key {id:123}	Read item by key	Item {id:123, name:'Book'}
3	Query	Condition status='active'	Search items matching condition	List of items with status='active'
4	End	-	-	Operations complete

💡 All operations complete successfully with data written, read, and queried.

Status Tracker

Variable	Start	After PutItem	After GetItem	After Query	Final
TableData	some items	{id:123, name:'Book'} added	No change	No change	{id:123, name:'Book'} present
RetrievedItem	none	none	{id:123, name:'Book'}	{id:123, name:'Book'}	{id:123, name:'Book'}
QueryResult	none	none	none	[items with status='active']	[items with status='active']

Key Moments - 2 Insights

Why does GetItem require a key but Query uses a condition?

GetItem uses a unique key to find exactly one item quickly (see step 2 in execution_table). Query searches by condition and can return multiple items (see step 3).

What happens if PutItem tries to add an item with an existing key?

PutItem will overwrite the existing item with the new data, as it writes directly to the key location (step 1).

Visual Quiz - 3 Questions

Look at the execution table, what is the output of the GetItem operation at step 2?

A Item {id:123, name:'Book'}

B List of items with status='active'

C Success confirmation

D No output

💡 Hint

Check the 'Output' column for step 2 in the execution_table.

At which step does the operation write data to the table?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Look at the 'Action' column to find where data is written.

If the Query condition changes to status='inactive', how does the QueryResult variable change after step 3?

A It becomes empty list

B It contains all items

C It contains items with status='inactive'

D It remains unchanged

💡 Hint

Refer to variable_tracker row 'QueryResult' after Query operation.

Concept Snapshot

PutItem writes or overwrites an item by key.
GetItem reads one item by its unique key.
Query searches items by condition, returning multiple matches.
Put and Get use keys; Query uses filters.
All operations interact with the database table.

Full Transcript

This visual execution shows how AWS data operations PutItem, GetItem, and Query work step-by-step. First, PutItem writes an item with a unique key to the table. Then, GetItem reads that item by its key, returning the exact data. Finally, Query searches the table for items matching a condition, returning a list of matching items. Variables track the table data and results after each operation. Key moments clarify why GetItem needs a key and how PutItem overwrites data. The quiz tests understanding of outputs and variable changes.

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