Lambda function with DynamoDB - Mini Project: Build & Apply

Lambda function with DynamoDB

📖 Scenario: You are building a simple AWS Lambda function that interacts with a DynamoDB table to store and retrieve user information. This is a common task when creating serverless applications that need to save data in the cloud.

🎯 Goal: Create a Lambda function that inserts a user record into a DynamoDB table and then retrieves it by user ID.

📋 What You'll Learn

Create a DynamoDB table data structure with exact user data

Add a configuration variable for the table name

Write the core logic to insert a user record into the DynamoDB table

Write the final code to retrieve the user record by user ID

💡 Why This Matters

🌍 Real World

Serverless applications often use AWS Lambda functions to interact with DynamoDB tables for storing and retrieving data without managing servers.

💼 Career

Understanding how to write Lambda functions that work with DynamoDB is essential for cloud developers and backend engineers working with AWS services.

1

DATA SETUP: Create a DynamoDB table data structure

Create a dictionary called dynamodb_table that represents a DynamoDB table with one user record. The user record must have these exact key-value pairs: 'UserID': 'user123', 'Name': 'Alice', and 'Age': 30.

DynamoDB

# Create the dynamodb_table dictionary with one user record
# Your code here

Hint

Use a dictionary where the key is the user ID and the value is another dictionary with the user details.

2

CONFIGURATION: Add a table name variable

Create a variable called table_name and set it to the string 'Users' to represent the DynamoDB table name.

DynamoDB

dynamodb_table = {
    'user123': {
        'UserID': 'user123',
        'Name': 'Alice',
        'Age': 30
    }
}
# Create the table_name variable and set it to 'Users'
# Your code here

Hint

This variable holds the name of the DynamoDB table you will use in your Lambda function.

3

CORE LOGIC: Insert a new user record

Write a function called insert_user that takes three parameters: user_id, name, and age. Inside the function, add a new entry to the dynamodb_table dictionary with the key as user_id and the value as a dictionary containing 'UserID', 'Name', and 'Age' with the given values.

DynamoDB

dynamodb_table = {
    'user123': {
        'UserID': 'user123',
        'Name': 'Alice',
        'Age': 30
    }
}
table_name = 'Users'
# Define the insert_user function to add a new user record
# Your code here

Hint

Use the function parameters to create a new dictionary and assign it to the dynamodb_table with the key user_id.

4

COMPLETION: Retrieve a user record by user ID

Write a function called get_user that takes one parameter user_id and returns the user record from dynamodb_table for that user_id. Use the get method of the dictionary to safely retrieve the record.

DynamoDB

dynamodb_table = {
    'user123': {
        'UserID': 'user123',
        'Name': 'Alice',
        'Age': 30
    }
}
table_name = 'Users'

def insert_user(user_id, name, age):
    dynamodb_table[user_id] = {
        'UserID': user_id,
        'Name': name,
        'Age': age
    }

# Define the get_user function to retrieve a user record by user_id
# Your code here

Hint

Use the dictionary get method to return the user record or null if not found.

Practice

1. What is the main purpose of using a Lambda function with DynamoDB in AWS?

easy

A. To run code automatically when DynamoDB data changes

B. To manually update DynamoDB tables from the AWS console

C. To create new DynamoDB tables without coding

D. To backup DynamoDB data to S3 manually

Solution

1. Step 1: Understand Lambda triggers

   Lambda functions can be triggered by events, such as changes in DynamoDB tables.

2. Step 2: Identify the purpose of automation

   This allows automatic code execution when data changes, without manual intervention.

3. Final Answer:

   To run code automatically when DynamoDB data changes -> Option A

4. Quick Check:

   Lambda triggers = automatic code run [OK]

Hint: Lambda runs code on events like DynamoDB changes [OK]

Common Mistakes:

• Thinking Lambda manually updates tables
• Confusing Lambda with backup tools
• Assuming Lambda creates tables automatically

2. Which of the following is the correct way to initialize AWS DynamoDB DocumentClient in a Node.js Lambda function?

easy

A. const docClient = new AWS.DynamoDBClient();

B. const docClient = new AWS.DynamoDB.DocumentClient();

C. const docClient = AWS.DynamoDB.DocumentClient();

D. const docClient = AWS.DynamoDB.Document();

Solution

1. Step 1: Recall correct DocumentClient syntax

   The AWS SDK requires using 'new' keyword to create a DocumentClient instance.

2. Step 2: Match correct class name and usage

   The correct class is AWS.DynamoDB.DocumentClient, not DynamoDBClient or Document.

3. Final Answer:

   const docClient = new AWS.DynamoDB.DocumentClient(); -> Option B

4. Quick Check:

   Use 'new' with DocumentClient class [OK]

Hint: Use 'new AWS.DynamoDB.DocumentClient()' to initialize [OK]

Common Mistakes:

• Omitting 'new' keyword
• Using wrong class name like DynamoDBClient
• Calling Document() instead of DocumentClient

3. Given this Lambda function snippet, what will be the output if the item with id '123' exists in the DynamoDB table?

const AWS = require('aws-sdk');
const docClient = new AWS.DynamoDB.DocumentClient();

exports.handler = async (event) => {
  const params = {
    TableName: 'Users',
    Key: { id: '123' }
  };
  const data = await docClient.get(params).promise();
  return data.Item;
};

medium

A. An error because 'get' method is incorrect

B. A list of all items in the Users table

C. An empty object {}

D. The item object with id '123' from the Users table

Solution

1. Step 1: Understand docClient.get usage

   The get method retrieves a single item by key from the specified table.

2. Step 2: Analyze the return value

   If the item with id '123' exists, data.Item will contain that item object.

3. Final Answer:

   The item object with id '123' from the Users table -> Option D

4. Quick Check:

   docClient.get returns item if found [OK]

Hint: docClient.get returns single item by key [OK]

Common Mistakes:

• Expecting a list instead of single item
• Thinking get method is invalid
• Assuming empty object if item exists

4. Identify the error in this Lambda function code that writes an item to DynamoDB:

const AWS = require('aws-sdk');
const docClient = new AWS.DynamoDB.DocumentClient();

exports.handler = async (event) => {
  const params = {
    TableName: 'Products',
    Item: {
      productId: '001',
      name: 'Book'
    }
  };
  await docClient.putItem(params).promise();
  return 'Success';
};

medium

A. Using 'putItem' instead of 'put' method on DocumentClient

B. Missing 'Key' property in params

C. TableName should be lowercase

D. Missing callback function in putItem

Solution

1. Step 1: Check DocumentClient method names

   DocumentClient uses 'put' method, not 'putItem'.

2. Step 2: Confirm correct method usage

   Using 'putItem' causes a runtime error because it does not exist on DocumentClient.

3. Final Answer:

   Using 'putItem' instead of 'put' method on DocumentClient -> Option A

4. Quick Check:

   Use 'put' to write items with DocumentClient [OK]

Hint: Use 'put', not 'putItem', with DocumentClient [OK]

Common Mistakes:

• Confusing low-level DynamoDB client with DocumentClient
• Assuming 'putItem' exists in DocumentClient
• Ignoring method naming conventions

5. You want a Lambda function to update a user's email in DynamoDB only if the user exists. Which approach correctly ensures this conditional update?

hard

A. Use docClient.delete before updating

B. Use docClient.put without any condition

C. Use docClient.update with ConditionExpression 'attribute_exists(id)'

D. Use docClient.get and then docClient.put unconditionally

Solution

1. Step 1: Understand conditional update in DynamoDB

   To update only if an item exists, use ConditionExpression with 'attribute_exists' on the key.

2. Step 2: Apply ConditionExpression in update method

   docClient.update supports ConditionExpression to prevent overwriting non-existing items.

3. Step 3: Evaluate other options

   Using put without condition overwrites or creates new items; delete before update is inefficient; get then put is not atomic.

4. Final Answer:

   Use docClient.update with ConditionExpression 'attribute_exists(id)' -> Option C

5. Quick Check:

   Conditional update = update + attribute_exists [OK]

Hint: Use ConditionExpression 'attribute_exists' for safe updates [OK]

Common Mistakes:

• Using put which overwrites without condition
• Deleting item before update unnecessarily
• Not using atomic conditional update