Andriy Slobodyanyk "How to Use Hibernate: Key Problems and Solutions"

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How to Use Hibernate:
Key Problems and Solutions
Andriy Slobodyanyk

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@Column(
name = "first_name",
length = 32,
nullable = false
)
private String firstName;
● Для чего нужен атрибут nullable?
● Можно ли создать и сохранить entity, если в поле name будет значение null?
● Проверяется ли длина поля?
● В чем отличие этих атрибутов @Column и
аннотаций @javax.validation.constraints.NotNull и @Size?
2

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https://dou.ua/lenta/articles/how-to-use-hibernate/

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Техническое задание

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• дата создания
• статус — новый, в обработке и т. д.
• срочность
• адрес доставки
• товары / количество
• цена с валютой товара
• клиент
5
Заказ

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@Entity
@Table(name = "orders")
public class OrderEntity {
@Id
private Long id;
private LocalDateTime created;
private String status; // see StatusConstants
private Integer express;
private String addressCity;
private String addressStreet;
private String addressBuilding;
private Long clientId;
}
@Entity
@Table(name = "items")
public class Item {
@Id
private Long id;
private String name;
private BigDecimal priceAmount;
private String priceCurrency;
}

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class Order {
LocalDateTime created;
Status status;
boolean express;
Address address;
Map<Item, Integer> items;
Client client;
}
class Address {
String city;
String street;
String building;
}
class Item {
String name;
Money price;
}
class Client {
String firstName;
String lastName;
}

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private Map<Item, Integer> items = new HashMap<>();
public Map<Item, Integer> getItems() {
return Collections.unmodifiableMap(items);
}
public void addItem(Item item) {
items.merge(item, 1, (v1, v2) -> v1 + v2);
}
public void removeItem(Item item) {
items.computeIfPresent(item, (k, v) -> v > 1 ? v - 1 : null);
}

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Подключаем JPA
● @Entity и @Id / @Embeddable
● Примитивы, числа, строки и даты
● @Enumerated и EnumType.ORDINAL / EnumType.STRING
● AttributeConverter
● @Type
● @ManyToOne, @OneToMany, @ElementCollection
● @Table
● @Column
11

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@Column -> DDL
12
@Column(
name = "first_name",
nullable = false,
length = 32
)
create table … (
first_name varchar(32) not null
)

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(Не)использование Id
13
boolean equals =
order.getId().equals(anotherOrder.getId());
boolean contains = orders.stream().anyMatch(
o -> .getId().equals(someOrder.getId());
select o from Order o where o.client.id =
:clientId
boolean equals = order.equals(anotherOrder);
boolean contains = orders.contains(someOrder);
select o from Order o where o.client = :client

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Эквивалентность (методы equals/hashCode)
14
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Order that = (Order) o;
return Objects.equals(id, that.id);
}
@Override
public int hashCode() {
return Objects.hash(id);
}
@Override
if (!(o instanceof Order)) return false;
Order order = (Order) o;
return Objects.equals(created, order.created)
&& Objects.equals(client, order.client);
}
@Override
return Objects.hash(created, client);
}
@Override
if (!(o instanceof Item)) return false;
Item that = (Item) o;
return Objects.equals(id, that.id);
}
@Override
return 31;
}

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Проблемы

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Проблемы
16
• Entity и DTO
• @Transient
• entityManager.detach()
• FetchType.EAGER
• EntityManager.flush() и clear()
• Lombok @Data

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MapStruct
17
@Mapper
public interface Mapper {
FooDto toDto(Foo foo);
}

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@Getter
@EqualsAndHashCode(of = {"firstName", "lastName"})
@ToString(of = {"firstName", "lastName"})
@NoArgsConstructor
@Entity
@Table(name = "clients")
public class Client {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@Column(length = 32, nullable = false)
private String lastName;
public Client(String firstName, String lastName) {
this.firstName = firstName;
this.lastName = lastName;
}
}
@Getter
@EqualsAndHashCode(of = "name")
@ToString(of = {"name", "price"})
@NoArgsConstructor
@Entity
@Table(name = "items")
public class Item {
@Id
private Long id;
@Column(nullable = false, length = 32)
private String name;
@Columns(
columns = {
@Column(name = "price_currency", length = 3, nullable = false),
@Column(name = "price_amount", precision = 7, scale = 2, nullable = false)
}
)
@Type(type = "org.jadira.usertype.moneyandcurrency.moneta.PersistentMoneyAmountAndCurrency")
private Money price;
public Item(String name, Money price) {
this.name = name;
this.price = price;
}
}

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1
@Getter
@EqualsAndHashCode(of = {"city", "street", "building"})
@ToString(of = {"city", "street", "building"})
@NoArgsConstructor
@AllArgsConstructor
@Embeddable
public class Address {
private String city;
private String street;
private String building;
}
@AllArgsConstructor
public enum Status {
NEW("N"),
PROCESSING("P"),
COMPLETED("C"),
DEFERRED("D");
@Getter
private final String code;
}
@Converter(autoApply = true)
public class StatusConverter implements
AttributeConverter<Status, String> {
@Override
public String convertToDatabaseColumn(Status status) {
return status.getCode();
}
@Override
public Status convertToEntityAttribute(String code) {
for (Status status : Status.values()) {
if (status.getCode().equals(code)) {
return status;
}
}
throw new IllegalArgumentException(
"Unknown code " + code
);
}
}

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2
@Getter
@EqualsAndHashCode(of = {"created", "client"})
@ToString(of = {"created", "address", "express", "status"})
@NoArgsConstructor
@Entity
@Table(name = "orders")
public class Order {
@Id
private Long id;
@Column(nullable = false)
private LocalDateTime created = LocalDateTime.now();
@AttributeOverrides({
@AttributeOverride(name = "city", column = @Column(name = "address_city", nullable = false, length = 32)),
@AttributeOverride(name = "street", column = @Column(name = "address_street", nullable = false, length = 32)),
@AttributeOverride(name = "building", column = @Column(name = "address_building", nullable = false, length = 32))
})
private Address address;
@Setter
private boolean express;
@Setter
private Status status = Status.NEW;
@ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.PERSIST, optional = false)
private Client client;
@ElementCollection
@Column(name = "quantity", nullable = false)
@MapKeyJoinColumn(name = "item_id")
@LazyCollection(LazyCollectionOption.EXTRA)
private Map<Item, Integer> items = new HashMap<>();
}

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Check List
22
● entities состоят из большого количества примитивных полей, а не из классов
● вместо enum-ов используются строковые константы
● методы equals/hashCode не определены
● в бизнес-логике и запросах фигурируют id
● происходит смешение Entity и Dto в одном классе
● использование FetchType.EAGER, в том числе по умолчанию в @ManyToOne
● ненужные вызовы flush() и clear()
● неаккуратное использование Lombok

Andriy Slobodyanyk "How to Use Hibernate: Key Problems and Solutions"

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