JPA - Beyond Copy-Paste

Transcript

1. @jkubrynski / kubrynski.com
   JPA - BEYOND COPY-PASTE
   JAKUB KUBRYNSKI
   jk@devskiller.com / @jkubrynski / http://kubrynski.com
   

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2. WHOAMI
   DEVSKILLER CO-FOUNDER
   BOTTEGA TRAINER
   DEVOXX.PL PROGRAM COMMITTEE
   SPRING CLOUD CONTRACT CO-AUTHOR
   

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4. ALL NON-TRIVIAL ABSTRACTIONS, TO SOME DEGREE, ARE LEAKY.
   JOEL SPOLSKY
   

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5. @Entity
   public class Product {
   @Id
   @GeneratedValue
   private Long id;
   @Column
   private String name;
   // ...
   }
   

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6. @Entity
   public class Product {
   @Id
   @GeneratedValue
   private Long id;
   @Column // it does exactly nothing
   private String name;
   // ...
   }
   

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7. @Transactional @Service
   public class ProductService {
   public void updatePrice(Long productId, Money newPrice) {
   Product product = productRepository.find(productId);
   product.setPrice(newPrice);
   productRepository.save(product);
   }
   }
   

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8. @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
   }
   }
   

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9. FIELDS VS GETTERS
   @Entity
   public class Product {
   private Long id;
   private String name;
   @Id
   public Long getId() {
   return id;
   }
   }
   

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10. MIXED ACCESS
    @Entity
    @Access(AccessType.FIELD)
    public class Product {
    private Long id;
    private String name;
    @Id
    @Access(AccessType.PROPERTY)
    public Long getId() {
    return id;
    }
    }
    

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11. @Entity
    public class Order {
    }
    

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12. @Entity(name = "orders")
    public class Order {
    }
    

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13. @Entity(name = "orders")
    public class Order {
    }
    insert into orders ...
    

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14. @Entity(name = "orders")
    public class Order {
    }
    em.createQuery("SELECT o FROM Order o")
    

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15. @Entity(name = "orders")
    public class Order {
    }
    em.createQuery("SELECT o FROM orders o")
    

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16. @Entity
    @Table(name = "orders")
    public class Order {
    }
    

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17. MAPPINGS
    

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18. ONE TO ONE
    @Entity
    public class Customer {
    @OneToOne
    private Address address;
    }
    @Entity
    public class Address {
    @OneToOne
    private Customer customer;
    }
    

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19. ONE TO ONE
    @Entity
    public class Customer {
    @OneToOne
    private Address address;
    }
    @Entity
    public class Address {
    @OneToOne(mappedBy = "address")
    private Customer customer;
    }
    

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20. ONE TO MANY
    @Entity
    public class Customer {
    @OneToMany
    private Set addresses;
    }
    

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21. ONE TO MANY
    @Entity
    public class Customer {
    @OneToMany
    @JoinColumn(name = "customer_id")
    private Set addresses;
    }
    

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22. MANY TO MANY
    @Entity
    public class Customer {
    @ManyToMany
    private Collection addresses;
    }
    @Entity
    public class Address {
    @ManyToMany
    private Collection customers;
    }
    

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23. LAZY LOADING
    element is loaded only when required
    proxy by subclassing, but not always
    needed
    

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24. LAZY LOADING
    Custom
    collections
    PersistentSet
    PersistentBag
    PersistentList
    

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25. SET, BAG OR LIST?
    @OneToMany
    Set products;
    

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26. SET, BAG OR LIST?
    @OneToMany
    List products;
    

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27. SET, BAG OR LIST?
    @OneToMany
    @OrderColumn
    List products;
    

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28. N+1
    @Entity
    public class User {
    @OneToMany
    private List addresses;
    }
    List users = em.createQuery("SELECT u FROM User u").getResultList();
    for (User user : users) {
    for (Address address : user.getAddresses()) {
    ...
    }
    }
    

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29. N+1
    @Entity
    public class User {
    @OneToMany
    @BatchSize(size = 10)
    private List addresses;
    }
    

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

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31. HOW TO SAVE
    EntityManager.persist()
    EntityManager.merge()
    

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32. OPTIMISTIC LOCKING
    @Entity
    public class User {
    @Version
    private int version;
    }
    

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33. OPTIMISTIC LOCKING IN REST
    NEVER HEARD OF IT
    

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34. IDENTITY
    EQUALS() AND HASHCODE()
    

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35. 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);
    }
    

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36. CACHING
    L1 - EntityManager cache / Session cache
    L2 - EntityManagerFactory cache / SessionFactory
    cache
    QueryCache
    

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37. FLUSH MODES
    MANUAL
    COMMIT
    AUTO
    ALWAYS
    

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38. LEVEL 1 CACHE PITFALLS
    FLUSH() AND CLEAR()
    

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39. LEVEL 2 CACHE PITFALLS
    DISTRIBUTED ENVIRONMENT
    

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40. HQL INJECTION
    String hqlQuery = "SELECT p FROM Product p where p.category = '" + cat + "'";
    List products = em.createQuery(hqlQuery, Product.class)
    .getResultList();
    

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41. MATERIALS
    Hibernate logs analysis
    Hibernate code debugging :-)
    https://leanpub.com/high-performance-java-
    persistence
    https://vladmihalcea.com
    http://www.jooq.org
    

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42. QUESTIONS?
    

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43. THANKS
    

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44. DYNAMIC UPDATES
    @Entity
    @DynamicUpdate
    public class MyEntity {
    // ...
    }
    

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45. DYNAMIC INSERTS
    @Entity
    @DynamicInsert
    public class MyEntity {
    // ...
    }
    

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