Module 4 - DynamoDB Scan

Learning Objectives

• Design and implement functionality that uses scan with a filter to retrieve a subset of items from a provided DynamoDB table
  Learn how to use scan operations with filter expressions to selectively retrieve items from a DynamoDB table based on specific criteria.

  // Create ScanExpression with filter
  DynamoDBScanExpression scanExpression = new DynamoDBScanExpression();
  
  // Create filter condition (products with price > 100)
  Map<String, AttributeValue> expressionValues = new HashMap<>();
  expressionValues.put(":priceValue", new AttributeValue().withN("100"));
  
  scanExpression.setFilterExpression("price > :priceValue");
  scanExpression.setExpressionAttributeValues(expressionValues);
  
  // Execute scan with filter
  PaginatedScanList<Product> productList = mapper.scan(Product.class, scanExpression);
  
  // Process filtered results
  for (Product product : productList) {
    System.out.println("Product: " + product.getName() + ", Price: " + product.getPrice());
  }
  
• Design and implement functionality that uses paginated scan with a limit to retrieve a subset of items from a provided DynamoDB table
  Learn how to implement efficient pagination for scan operations to process large datasets in manageable chunks, reducing memory usage and improving application responsiveness.

  // Create scan expression with limit
  DynamoDBScanExpression scanExpression = new DynamoDBScanExpression()
    .withLimit(10); // Retrieve 10 items per page
  
  Map<String, AttributeValue> lastKeyEvaluated = null;
  
  do {
    // Set exclusive start key (for pagination)
    scanExpression.setExclusiveStartKey(lastKeyEvaluated);
  
    // Execute scan
    ScanResultPage<Product> scanResult = mapper.scanPage(Product.class, scanExpression);
  
    // Process current page of results
    for (Product product : scanResult.getResults()) {
      System.out.println("Processing: " + product.getId());
    }
  
    // Get last evaluated key for next page
    lastKeyEvaluated = scanResult.getLastEvaluatedKey();
  
    // Continue until no more pages
  } while (lastKeyEvaluated != null);
  
• Outline when to scan a DynamoDB table
  Understand the appropriate use cases for scan operations, including full table exports, infrequent operations on small tables, or when you need to query data without a known partition key.
• Outline how to use DynamoDBMapper's scan() method
  Learn the different methods and options available in DynamoDBMapper for scan operations, including basic scans, filtered scans, and paginated scans.

  // Basic scan (all items)
  PaginatedScanList<User> allUsers = mapper.scan(User.class, new DynamoDBScanExpression());
  
  // Scan with attribute projection (specific attributes only)
  DynamoDBScanExpression scanExpression = new DynamoDBScanExpression()
    .withProjectionExpression("id, username, email");
  
  // Parallel scan (for large tables)
  DynamoDBScanExpression parallelScanExpression = new DynamoDBScanExpression()
    .withSegment(0) // Current segment
    .withTotalSegments(4); // Total segments