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beginner Phase · REST API Development

Filtering

Design query parameter filtering for REST APIs.

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Filtering Patterns

Query Parameter Filtering

GET /products?category=electronics
GET /products?minPrice=100&maxPrice=500
GET /products?brand=Apple&inStock=true

Filter Types

Type Example Use Case
Equality ?status=active Exact match
Range ?minPrice=100&maxPrice=500 Numeric ranges
Contains ?name=laptop Text search
List ?category=phone,tablet Multiple values
Date range ?from=2025-01-01&to=2025-12-31 Time periods
Boolean ?inStock=true True/false flags

Advanced Filtering

# Nested filters
GET /products?category.name=electronics&category.level=2

# Multiple values (OR)
GET /products?status=active,pending

# Negation
GET /products?status=!cancelled

# Array contains
GET /products?tags=wireless,bluetooth

Filtering Implementation

@GetMapping("/products")
public ResponseEntity<List<Product>> getProducts(
    @RequestParam(required = false) String category,
    @RequestParam(required = false) BigDecimal minPrice,
    @RequestParam(required = false) BigDecimal maxPrice,
    @RequestParam(required = false) Boolean inStock,
    Pageable pageable) {

    return ResponseEntity.ok(
        productService.filter(category, minPrice, maxPrice, inStock, pageable)
    );
}

Best Practices

Key Principles

  1. Follow SOLID principles
  2. Write clean, readable code
  3. Test thoroughly
  4. Document decisions
  5. Monitor in production

Implementation

  • Start simple, refactor as needed
  • Use established patterns
  • Consider trade-offs
  • Review with peers

Continuous Improvement

  • Learn from incidents
  • Update documentation
  • Share knowledge
  • Mentor others

Key Points

  • Understanding Filtering is essential for production systems
  • Always consider scalability and maintainability
  • Test thoroughly before deploying to production
  • Monitor performance and set up alerting

Common Patterns

  1. Validation: Always validate input at the boundary
  2. Error Handling: Use structured error responses
  3. Logging: Log key events for debugging
  4. Testing: Unit, integration, and load tests
  5. Documentation: Keep docs updated with code changes

Practice Problems

0 / 3 solved
Implement Filtering

Design and implement a solution for Filtering in a backend system. Consider scalability, error handling, and production readiness.

Solution 
// Filtering implementation
// Key aspects: validation, error handling, logging, testing

public class Filtering {
    // Production-ready implementation
}
Filtering Edge Cases

Identify and handle edge cases for Filtering. What happens under high load, with invalid input, or during failures?

Solution 
// Edge case handling:
// 1. Null/empty input -> validation
// 2. High load -> rate limiting, queuing
// 3. Failures -> retries, circuit breaker
// 4. Concurrent access -> locks, idempotency
Filtering Testing Strategy

Write a testing strategy for Filtering. Include unit tests, integration tests, and performance tests.

Solution 
// Test plan:
// - Unit: 80% coverage target
// - Integration: API contracts
// - Performance: latency, throughput
// - Chaos: failure injection

Quiz

1. How should multiple filter values for the same field be handled?

Question 1 options

2. Which filtering pattern is most RESTful?

Question 2 options

3. What is a common mistake when implementing Filtering?

Question 3 options

Flashcards

Question

RESTful filtering pattern?

Click to reveal answer

Answer

GET /resource?field=value (query parameters)

Question

How to handle multiple filter values?

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Answer

Comma-separated: ?status=active,pending

Question

Filtering best practices

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Answer

Follow SOLID principles, write clean code, test thoroughly, document decisions, and monitor in production.

Revision Notes

Key Takeaways

  • 1. Use query parameters for filtering: /products?category=electronics
  • 2. Support equality, range, list, and boolean filters
  • 3. Combine filtering with pagination and sorting
  • 4. Make all filter parameters optional

Interview Tips

  • • Design filtering for a given scenario
  • • Know how to handle complex filter combinations

Cheat Sheet

Filtering

  • Equality: ?status=active
  • Range: ?minPrice=100&maxPrice=500
  • List: ?category=phone,tablet
  • Boolean: ?inStock=true
  • Rule: All filters optional, GET with query params