Filter expressions in DynamoDB - Mini Project: Build & Apply

Filter Items in DynamoDB Using Filter Expressions

📖 Scenario: You manage a DynamoDB table that stores information about books in a library. You want to find books that are currently available for borrowing.

🎯 Goal: Build a DynamoDB query that uses a filter expression to retrieve only the books where the available attribute is true.

📋 What You'll Learn

Create a dictionary called table representing the DynamoDB table with sample book items.

Add a filter expression variable called filter_expression to select books where available is true.

Write a query using the scan method with the filter expression to get only available books.

Complete the query setup by including the filter expression in the scan parameters.

💡 Why This Matters

🌍 Real World

Filtering data in DynamoDB tables is common when you want to retrieve only items that meet certain conditions, such as available products or active users.

💼 Career

Understanding filter expressions is essential for backend developers and database administrators working with AWS DynamoDB to optimize data retrieval and reduce costs.

1

Create the DynamoDB table data

Create a dictionary called table with a key Items containing a list of three book dictionaries. Each book dictionary must have these exact keys and values: {'title': 'Book A', 'author': 'Author 1', 'available': True}, {'title': 'Book B', 'author': 'Author 2', 'available': False}, and {'title': 'Book C', 'author': 'Author 3', 'available': True}.

DynamoDB

# Create the DynamoDB table data with three books
# Your code here

Need a hint?

Use a dictionary with key 'Items' and a list of dictionaries for the books.

2

Define the filter expression

Create a variable called filter_expression and set it to the string 'available = :val' to filter books where the available attribute is true.

DynamoDB

table = {
    'Items': [
        {'title': 'Book A', 'author': 'Author 1', 'available': True},
        {'title': 'Book B', 'author': 'Author 2', 'available': False},
        {'title': 'Book C', 'author': 'Author 3', 'available': True}
    ]
}
# Define the filter expression to select available books
# Your code here

Need a hint?

The filter expression is a string that compares available to a placeholder :val.

3

Write the scan query with filter expression

Create a dictionary called scan_params with keys FilterExpression set to filter_expression and ExpressionAttributeValues set to a dictionary with ':val' as True.

DynamoDB

table = {
    'Items': [
        {'title': 'Book A', 'author': 'Author 1', 'available': True},
        {'title': 'Book B', 'author': 'Author 2', 'available': False},
        {'title': 'Book C', 'author': 'Author 3', 'available': True}
    ]
}
filter_expression = 'available = :val'
# Create scan parameters with filter expression and attribute values
# Your code here

Need a hint?

Use a dictionary with keys FilterExpression and ExpressionAttributeValues for the scan parameters.

4

Complete the scan query setup

Add a variable called result and set it to the result of calling table['Items'] filtered by the condition where the available attribute is True using the scan_params filter expression logic.

DynamoDB

table = {
    'Items': [
        {'title': 'Book A', 'author': 'Author 1', 'available': True},
        {'title': 'Book B', 'author': 'Author 2', 'available': False},
        {'title': 'Book C', 'author': 'Author 3', 'available': True}
    ]
}
filter_expression = 'available = :val'
scan_params = {
    'FilterExpression': filter_expression,
    'ExpressionAttributeValues': {':val': True}
}
# Filter the items manually to simulate scan with filter expression
# Your code here

Need a hint?

Use a list comprehension to filter table['Items'] where available equals True.