Hibernate и JPA: ORM в Java

1@Entity
2@Table(name = "users")
3@Getter @Setter @NoArgsConstructor
4public class User {
5
6    @Id
7    @GeneratedValue(strategy = GenerationType.IDENTITY)
8    private Long id;
9
10    @Column(nullable = false, length = 100)
11    private String name;
12
13    @Column(unique = true, nullable = false)
14    private String email;
15
16    @Enumerated(EnumType.STRING)
17    @Column(nullable = false)
18    private UserStatus status;
19
20    @CreationTimestamp
21    private LocalDateTime createdAt;
22
23    @UpdateTimestamp
24    private LocalDateTime updatedAt;
25
26    @OneToMany(mappedBy = "user", cascade = CascadeType.ALL, orphanRemoval = true)
27    private List<Order> orders = new ArrayList<>();
28
29    @ManyToOne(fetch = FetchType.LAZY)
30    @JoinColumn(name = "department_id")
31    private Department department;
32}

1@Entity
2public class UserProfile {
3    @OneToOne(fetch = FetchType.LAZY)
4    @JoinColumn(name = "user_id")
5    private User user;
6
7    @OneToOne(mappedBy = "profile", cascade = CascadeType.ALL)
8    private Address address;
9}

1@Entity
2public class Order {
3    @ManyToOne(fetch = FetchType.LAZY)
4    @JoinColumn(name = "user_id", nullable = false)
5    private User user;
6
7    @OneToMany(mappedBy = "order", cascade = CascadeType.ALL)
8    private List<OrderItem> items = new ArrayList<>();
9}

1@Entity
2public class Student {
3    @ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
4    @JoinTable(
5        name = "student_course",
6        joinColumns = @JoinColumn(name = "student_id"),
7        inverseJoinColumns = @JoinColumn(name = "course_id")
8    )
9    private Set<Course> courses = new HashSet<>();
10}

1// N+1 проблема: 1 запрос на пользователей + N запросов на заказы
2List<User> users = userRepository.findAll();
3users.forEach(u -> u.getOrders().size()); // LazyInitializationException

1@Query("SELECT u FROM User u JOIN FETCH u.orders WHERE u.id = :id")
2User findUserWithOrders(@Param("id") Long id);

1// JPQL запрос
2@Query("SELECT u FROM User u WHERE u.status = :status AND u.createdAt > :date")
3List<User> findActiveUsersAfter(@Param("status") UserStatus status,
4                                 @Param("date") LocalDateTime date);
5
6// Native SQL запрос
7@Query(value = "SELECT * FROM users u WHERE u.email LIKE %:domain%",
8       nativeQuery = true)
9List<User> findByEmailDomain(@Param("domain") String domain);

1CriteriaBuilder cb = entityManager.getCriteriaBuilder();
2CriteriaQuery<User> query = cb.createQuery(User.class);
3Root<User> user = query.from(User.class);
4
5query.select(user)
6    .where(
7        cb.equal(user.get("status"), UserStatus.ACTIVE),
8        cb.greaterThan(user.get("createdAt"), LocalDateTime.now().minusDays(30))
9    )
10    .orderBy(cb.desc(user.get("createdAt")));
11
12List<User> results = entityManager.createQuery(query).getResultList();

1@Entity
2@Cacheable
3@org.hibernate.annotations.Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
4public class User {
5    // ...
6}

1@OneToMany(mappedBy = "user")
2@BatchSize(size = 25)
3private List<Order> orders;

1// Interface-based projection
2public interface UserSummary {
3    String getName();
4    String getEmail();
5}
6
7@Query("SELECT u.name as name, u.email as email FROM User u")
8List<UserSummary> findAllSummaries();

1@Service
2public class OrderService {
3
4    @Transactional
5    public Order createOrder(CreateOrderRequest request) {
6        User user = userRepository.findById(request.getUserId())
7            .orElseThrow(() -> new RuntimeException("User not found"));
8
9        Order order = new Order(user, request.getItems());
10        return orderRepository.save(order);
11    }
12
13    @Transactional(readOnly = true)
14    public Order getOrder(Long id) {
15        return orderRepository.findById(id)
16            .orElseThrow(() -> new RuntimeException("Order not found"));
17    }
18}