Repository

The repository layer handles all database operations. Spring Data JPA makes this incredibly simple.

Repository Interface

@Repository
public interface ProductRepository extends JpaRepository<Product, Long> {
    // Spring Data JPA auto-implements these methods:
    // save(), findById(), findAll(), deleteById(), count(), existsById()
}

Just by extending JpaRepository, you get all CRUD operations for free.

Custom Query Methods

Spring Data JPA derives queries from method names:

@Repository
public interface ProductRepository extends JpaRepository<Product, Long> {

    Optional<Product> findByName(String name);
    List<Product> findByCategoryId(Long categoryId);
    List<Product> findByPriceBetween(BigDecimal min, BigDecimal max);
    List<Product> findByNameContainingIgnoreCase(String keyword);
}

JPQL Queries

For complex queries, use @Query with JPQL:

@Repository
public interface ProductRepository extends JpaRepository<Product, Long> {

    @Query("SELECT p FROM Product p WHERE p.category.name = :categoryName AND p.price < :maxPrice")
    List<Product> findByCategoryAndMaxPrice(@Param("categoryName") String categoryName,
                                            @Param("maxPrice") BigDecimal maxPrice);
}

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 Repository 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