Limit and pagination in DynamoDB - Mini Project: Build & Apply

Limit and Pagination in DynamoDB Queries

📖 Scenario: You are building a simple product catalog using DynamoDB. The catalog contains many products, but you want to show only a few products at a time to users. This is like flipping pages in a book, where each page shows a limited number of products.

🎯 Goal: Build a DynamoDB query that retrieves products with a limit on how many items to fetch, and supports pagination by using the last evaluated key to get the next set of products.

📋 What You'll Learn

Create a dictionary called query_params with the table name and key condition expression.

Add a Limit key to query_params to restrict the number of items returned.

Use a variable called last_evaluated_key to store the pagination token.

Add ExclusiveStartKey to query_params when last_evaluated_key is not None.

Write the DynamoDB query call using query_params.

💡 Why This Matters

🌍 Real World

Pagination is essential in real-world applications to avoid loading too much data at once and to improve user experience by showing data in manageable chunks.

💼 Career

Understanding DynamoDB pagination is important for backend developers working with AWS to build scalable and efficient data-driven applications.

1

Set up the initial query parameters

Create a dictionary called query_params with 'TableName': 'Products', 'KeyConditionExpression': 'Category = :cat', and 'ExpressionAttributeValues': {':cat': 'Books'}.

DynamoDB

# Create query_params dictionary with TableName, KeyConditionExpression, and ExpressionAttributeValues
# Your code here

Need a hint?

Remember to create query_params as a dictionary with the exact keys and values.

2

Add a limit to the query

Add a key 'Limit' with the value 5 to the existing query_params dictionary.

DynamoDB

query_params = {
    'TableName': 'Products',
    'KeyConditionExpression': 'Category = :cat',
    'ExpressionAttributeValues': {':cat': 'Books'}
}
# Add a Limit of 5 to query_params
# Your code here

Need a hint?

Use query_params['Limit'] = 5 or add it directly in the dictionary.

3

Set up pagination with last evaluated key

Create a variable called last_evaluated_key and set it to None. Then add an if statement that checks if last_evaluated_key is not None. Inside the if, add 'ExclusiveStartKey' to query_params with the value last_evaluated_key.

DynamoDB

query_params = {
    'TableName': 'Products',
    'KeyConditionExpression': 'Category = :cat',
    'ExpressionAttributeValues': {':cat': 'Books'},
    'Limit': 5
}
# Create last_evaluated_key variable and add ExclusiveStartKey if it is not None
# Your code here

Need a hint?

Use last_evaluated_key = None and an if to add ExclusiveStartKey only when needed.

4

Write the DynamoDB query call

Assuming you have a DynamoDB client called dynamodb_client, write a line that calls dynamodb_client.query() with **query_params and assign the result to a variable called response.

DynamoDB

query_params = {
    'TableName': 'Products',
    'KeyConditionExpression': 'Category = :cat',
    'ExpressionAttributeValues': {':cat': 'Books'},
    'Limit': 5
}
last_evaluated_key = None
if last_evaluated_key is not None:
    query_params['ExclusiveStartKey'] = last_evaluated_key

# Call dynamodb_client.query with query_params and save to response
# Your code here

Need a hint?

Use the query method of dynamodb_client with unpacked query_params.