@Repository

@Repository — Data Access Layer

@Repository
public interface OrderRepository extends JpaRepository<Order, Long> {

    List<Order> findByCustomerId(Long customerId);

    @Query("SELECT o FROM Order o WHERE o.status = :status")
    List<Order> findByStatus(@Param("status") OrderStatus status);

    @Modifying
    @Query("UPDATE Order o SET o.status = :status WHERE o.id = :id")
    int updateStatus(@Param("id") Long id, @Param("status") OrderStatus status);
}

What @Repository Provides

1. Exception translation — Converts JDBC exceptions to Spring exceptions
2. Component scanning — Auto-detected by Spring
3. Persistence exception translation — Wraps DataAccessException

Spring Data JPA Methods

Method	Purpose	Example
findById()	Get by primary key	repo.findById(1L)
findAll()	Get all records	repo.findAll()
save()	Create or update	repo.save(entity)
deleteById()	Delete by ID	repo.deleteById(1L)
count()	Count records	repo.count()
existsById()	Check existence	repo.existsById(1L)

Derived Query Methods

public interface ProductRepository extends JpaRepository<Product, Long> {

    // Method name conventions
    List<Product> findByCategory(String category);
    List<Product> findByPriceBetween(BigDecimal min, BigDecimal max);
    List<Product> findByNameContainingIgnoreCase(String name);
    List<Product> findByCategoryAndPriceLessThan(String category, BigDecimal price);
    Optional<Product> findBySku(String sku);
}

Configuration

• Use properties over YAML for simple configs
• Externalize configuration
• Use profiles for environments
• Validate on startup

Bean Management

• Prefer constructor injection
• Use appropriate scope
• Implement lazy initialization
• Clean up resources

Security

• Use Spring Security
• Implement CSRF protection
• Use method-level security
• Log security events

Key Points

• Understanding @Repository Annotation 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