Paginasi, Pengurutan, dan Proyeksi

Mengapa Menggunakan Paginasi?

Pageable dan PageRequest

Pageable pageable = PageRequest.of(0, 20); // page 0, 20 per page
Page<User> page = userRepo.findAll(pageable);
System.out.println("Total: " + page.getTotalElements());
System.out.println("Pages: " + page.getTotalPages());
System.out.println("Content: " + page.getContent().size());

Pengurutan dengan PageRequest

Pageable sorted = PageRequest.of(0, 20,
    Sort.by(Sort.Direction.DESC, "createdAt")
        .and(Sort.by("name")));
Page<User> page = userRepo.findAll(sorted);

Potongan vs Page

public interface UserRepository extends JpaRepository<User, Long> {
    Slice<User> findByStatus(UserStatus status, Pageable pageable);
}

Integrasi Spring MVC

@GetMapping("/users")
public Page<UserDto> list(Pageable pageable) {
    return userRepo.findAll(pageable).map(UserDto::from);
}
// GET /users?page=0&size=10&sort=name,asc

Proyeksi Antarmuka

public interface UserSummary {
    Long getId();
    String getName();
    String getEmail();
}
List<UserSummary> findByStatus(UserStatus status);

Proyeksi Berbasis Kelas (DTO)

public record UserDto(Long id, String name, String email) {}

@Query("SELECT new com.example.UserDto(u.id, u.name, u.email) FROM User u WHERE u.status = :s")
List<UserDto> findSummaries(@Param("s") UserStatus status);

Proyeksi Dinamis

public interface UserRepository extends JpaRepository<User, Long> {
    <T> List<T> findByStatus(UserStatus status, Class<T> type);
}
// Usage:
List<UserSummary> summaries = repo.findByStatus(ACTIVE, UserSummary.class);
List<User>        full      = repo.findByStatus(ACTIVE, User.class);

Paginasi Berbasis Kunci (Offset vs Keyset)

// Keyset pagination:
@Query("SELECT u FROM User u WHERE u.id > :lastId ORDER BY u.id LIMIT :size")
List<User> findPage(@Param("lastId") Long lastId, @Param("size") int size);

Optimasi Jumlah Total

@Query(value = "SELECT u FROM User u JOIN FETCH u.orders WHERE u.status = :s",
       countQuery = "SELECT COUNT(u) FROM User u WHERE u.status = :s")
Page<User> findActiveWithOrders(@Param("s") UserStatus s, Pageable p);

Mengembalikan ResponseEntity dengan Metadata Halaman

@GetMapping("/users")
public ResponseEntity<Map<String, Object>> list(Pageable p) {
    Page<UserDto> page = repo.findAll(p).map(UserDto::from);
    return ResponseEntity.ok(Map.of(
        "content", page.getContent(),
        "totalElements", page.getTotalElements(),
        "totalPages", page.getTotalPages()
    ));
}

Pemeriksaan Singkat

Ringkasan