@jkubrynski / kubrynski.com

JPA - BEYOND COPY-PASTEJAKUB KUBRYNSKI

jk@devskiller.com / @jkubrynski / http://kubrynski.com

WHOAMICO-FOUNDER OF DEVSKILLER / CODEARTE

TRAINER AT BOTTEGA

DEVOXX.PL PROGRAM COMMITTEE

FORMER CONFITURA.PL

@Entitypublic class Product

@Id @GeneratedValue private Long id;

@Column private String name;

// ...

@Entitypublic class Product

@Id @GeneratedValue private Long id;

@Column // it does exactly nothing private String name;

// ...

@Transactional @Service public class ProductService

public void updatePrice(Long productId, Money newPrice) Product product = productRepository.find(productId); product.setPrice(newPrice); productRepository.save(product);

@Transactional @Service public class ProductService

public void updatePrice(Long productId, Money newPrice) Product product = productRepository.find(productId); product.setPrice(newPrice); productRepository.save(product); // it does exactly nothing

FIELDS VS GETTERS@Entitypublic class Product

private Long id;

private String name;

@Id public Long getId() return id;

MIXED ACCESS@Entity@Access(AccessType.FIELD) public class Product

private Long id;

private String name;

@Id @Access(AccessType.PROPERTY) public Long getId() return id;

@Entitypublic class Order

@Entity(name = "orders") public class Order

@Entity(name = "orders") public class Order

insert into orders ...

@Entity(name = "orders") public class Order

em.createQuery("SELECT o FROM Order o")

@Entity(name = "orders") public class Order

em.createQuery("SELECT o FROM orders o")

@Entity@Table(name = "orders") public class Order

ONE TO ONE@Entitypublic class Customer

@OneToOne private Address address;

@Entitypublic class Address

@OneToOne private Customer customer;

ONE TO ONE@Entitypublic class Customer

@OneToOne private Address address;

@Entitypublic class Address

@OneToOne(mappedBy = "address") private Customer customer;

ONE TO MANY@Entitypublic class Customer

@OneToMany private Set<Address> addresses;

ONE TO MANY@Entitypublic class Customer

@OneToMany @JoinColumn(name = "customer_id") private Set<Address> addresses;

MANY TO MANY@Entitypublic class Customer

@ManyToMany private Collection<Address> addresses;

@Entitypublic class Address

@ManyToMany private Collection<Customer> customers;

LAZY LOADINGelement is loaded only when requiredproxy by subclassing, but not always needed

LAZY LOADINGCustom collections

PersistentSetPersistentBagPersistentList

SET, BAG OR LIST?@OneToMany Set<Product> products;

SET, BAG OR LIST?@OneToMany List<Product> products;

SET, BAG OR LIST?@OneToMany @OrderColumn List<Product> products;

N+1@Entitypublic class User

@OneToMany private List<Address> addresses;

List<User> users = em.createQuery("SELECT u FROM User u").getResultList();

for (User user : users) for (Address address : user.getAddresses()) ...

N+1@Entitypublic class User

@OneToMany @BatchSize(size = 10) private List<Address> addresses;

N+1SELECT DISTINCT u FROM User u JOIN FETCH u.addresses

HOW TO SAVEEntityManager.persist()EntityManager.merge()

OPTIMISTIC LOCKING@Entitypublic class User

@Version private int version;

OPTIMISTIC LOCKING IN RESTNEVER HEARD OF IT

IDENTITYEQUALS() AND HASHCODE()

BASE CLASS@MappedSuperclass public abstract class BaseEntity implements Serializable

@Id @GeneratedValue private Long id;

private String uuid = UUID.randomUUID().toString();

public int hashCode() return Objects.hash(uuid);

public boolean equals(Object that) return this == that || that instanceof BaseEntity && Objects.equals(uuid, ((BaseEntity) that).uuid);

CACHINGL1 - EntityManager cache / Session cacheL2 - EntityManagerFactory cache / SessionFactory cacheQueryCache

FLUSH MODESMANUALCOMMITAUTOALWAYS

LEVEL 1 CACHE PITFALLSFLUSH() AND CLEAR()

LEVEL 2 CACHE PITFALLSDISTRIBUTED ENVIRONMENT

HQL INJECTIONString hqlQuery = "SELECT p FROM Product p where p.category = '" + cat + "'";

List<Product> products = em.createQuery(hqlQuery, Product.class) .getResultList();

DYNAMIC UPDATES@Entity@DynamicUpdate public class MyEntity // ...

DYNAMIC INSERTS@Entity@DynamicInsert public class MyEntity // ...

QUESTIONS?

THANKS