如何在SpringBoot中使用Hibernate/JPA的@NaturalId？

banq發表於2019-02-10
Spring Boot

第一步，在實體中標記你的業務欄位為@NaturalId：


@Entity
public class Product implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;

    @NaturalId(mutable = false)
    @Column(nullable = false, updatable = false, unique = true, length = 50)
    private String code;

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (!(o instanceof Product)) {
            return false;
        }
        Product naturalIdProduct = (Product) o;
        return Objects.equals(getCode(), naturalIdProduct.getCode());
        // including sku 
        // return Objects.equals(getCode(), naturalIdProduct.getCode())
            // && Objects.equals(getSku(), naturalIdProduct.getSku());
    }

    @Override
    public int hashCode() {
        return Objects.hash(getCode());
        // including sku
        // return Objects.hash(getCode(), getSku());
    }

    @Override
    public String toString() {
        return "Product{" + "id=" + id + ", name=" + name + ", code=" + code + '}';
        // including sku
        // return "Product{" + "id=" + id + ", name=" + name + ", code=" + code + ", sku=" + sku + '}';
    }


這裡的code欄位標記為@NaturalId，注意點：

 對於非可變id，將列標記為@NaturalId(mutable = false)和@Column(nullable = false, updatable = false, unique = true, ...)

對於可變id，將列標記為@NaturalId(mutable = true)和@Column(nullable = false, updatable = true, unique = true, ...)

使用NaturalId重寫覆蓋equals()並hashCode()方法

第二步，需要定義@NoRepositoryBean介面（NaturalRepository），在其中定義兩個方法，命名findBySimpleNaturalId()和findByNaturalId() 


@NoRepositoryBean
public interface NaturalRepository<T, ID extends Serializable> extends JpaRepository<T, ID> {

    // use this method when your entity has a single field annotated with @NaturalId
    Optional<T> findBySimpleNaturalId(ID naturalId);
     
    // use this method when your entity has more than one field annotated with @NaturalId
    Optional<T> findByNaturalId(Map<String, Object> naturalIds);        
}


第三步， 實現此介面（NaturalRepositoryImpl），其中依賴使用Hibernate, Session, bySimpleNaturalId()和 byNaturalId() 方法。


@Transactional(readOnly = true)
public class NaturalRepositoryImpl<T, ID extends Serializable>
        extends SimpleJpaRepository<T, ID> implements NaturalRepository<T, ID> {

    private final EntityManager entityManager;

    public NaturalRepositoryImpl(JpaEntityInformation entityInformation,
            EntityManager entityManager) {
        super(entityInformation, entityManager);

        this.entityManager = entityManager;
    }

    @Override
    public Optional<T> findBySimpleNaturalId(ID naturalId) {

        Optional<T> entity = entityManager.unwrap(Session.class)
                .bySimpleNaturalId(this.getDomainClass())
                .loadOptional(naturalId);

        return entity;
    }

    @Override
    public Optional<T> findByNaturalId(Map<String, Object> naturalIds) {

        NaturalIdLoadAccess<T> loadAccess
                = entityManager.unwrap(Session.class).byNaturalId(this.getDomainClass());
        naturalIds.forEach(loadAccess::using);

        return loadAccess.loadOptional();
    }

}


第四步：在SpringBoot入口類中使用@EnableJpaRepositories(repositoryBaseClass = NaturalRepositoryImpl.class)註冊此實施為基類


@SpringBootApplication
@EnableJpaRepositories(repositoryBaseClass = NaturalRepositoryImpl.class)
public class NaturalIdApplication {


第五步：對於實體​​，編寫一個經典的儲存庫：

@Repository
public interface ProductRepository<T, ID> extends NaturalRepository<Product, Long>{    
}


第六步：在您的服務中注入此類並呼叫findBySimpleNaturalId()或findByNaturalId()


@SpringBootApplication
@EnableJpaRepositories(repositoryBaseClass = NaturalRepositoryImpl.class)
public class NaturalIdApplication {

    private static final Logger logger = Logger.getLogger(NaturalIdApplication.class.getName());

    private final ProductRepository productRepository;

    public NaturalIdApplication(ProductRepository productRepository) {
        this.productRepository = productRepository;
    }

    public static void main(String[] args) {
        SpringApplication.run(NaturalIdApplication.class, args);
    }

    @Bean
    public ApplicationRunner init() {
        return args -> {

            // persist two products
            Product tshirt = new Product();
            tshirt.setName("T-Shirt");
            tshirt.setCode("014-tshirt-2019");
            // tshirt.setSku(1L);

            Product socks = new Product();
            socks.setName("Socks");
            socks.setCode("012-socks-2018");
            // socks.setSku(2L);

            productRepository.save(tshirt);
            productRepository.save(socks);

            Optional<Product> p1 = productRepository.findById(tshirt.getId());                 // find by ID
            Optional<Product> p2 = productRepository.findBySimpleNaturalId(tshirt.getCode()); // find by natural ID

            if (p1.isPresent() && p2.isPresent()) {
                System.out.println("p1: " + p1.get());
                System.out.println("p2: " + p2.get());
            } else {
                System.out.println("Not found!");
            }
        };
    }
}


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