java - 级联属性导致的分离实体错误

Question

我是 JPA 和 Hibernate 的新手。我有两个实体:供应商和产品，如下所述。

@Entity
public class Vendor extends BaseEntity
{
    private static final long serialVersionUID = 267250313080292374L;

    @NotNull
    private String name;

    @NotNull
    private String city;

    @OneToMany(mappedBy = "vendor", cascade = CascadeType.ALL)
    private List<Product> products = new ArrayList<Product>();

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public List<Product> getProducts() {
        return products;
    }

    public void setProducts(List<Product> products) {
        this.products = products;
    }
}

@Entity
public class Product extends BaseEntity
{
    private static final long serialVersionUID = -4676899182130380017L;

    @NotNull
    private String name;

    @Column(nullable = false, precision = 10, scale = 2)
    private double price;

    @NotNull
    private int quantity;

    @ManyToOne(cascade = CascadeType.ALL)
    @JoinColumn(name="VENDOR_ID", nullable = false)
    private Vendor vendor;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public int getQuantity() {
        return quantity;
    }

    public void setQuantity(int quantity) {
        this.quantity = quantity;
    }

    public Vendor getVendor() {
        return vendor;
    }

    public void setVendor(Vendor vendor) {
        this.vendor = vendor;
    }
}

我的问题与 @ManyToOne 注释中属性 nullable = false 的使用有关。我希望用 @ManyToOne 注释的相应列不为空。但是，当我使用以下测试来测试实体的持久性时:

public void testCreateEntity()
{

        // create vendor1, set name and city
        vendor1 = new Vendor();
        vendor1.setName("MediaMarkt");
        vendor1.setCity("Berlin");
        vendor1 = service.createOrUpdateEntity(vendor1);

        //  create product1, set name, price and quantity
        product1 = new Product();
        product1.setName("Samsung Galaxy S7");
        product1.setPrice(new Double("819.00"));
        product1.setQuantity(1);

        vendor1.getProducts().add(product1);
        product1.setVendor(vendor1);

        //  create product at service
        product1 = service.createOrUpdateEntity(product1);
...
}

其中 createOrUpdateEntity 方法是 DAO Bean 对象的一部分

 @PersistenceContext
 private EntityManager em;

    public <T extends BaseEntity> T createOrUpdateEntity(T entity)
    {
        // as we have no id yet, it must be freshly brewed
        if (entity.getId() == 0)
        {
            log.debug("createOrUpdateEntity::create:: {}", entity);
            this.em.persist(entity);
        }
        // if there is an id, we must have dealt with it before
        else
        {
            log.debug("createOrUpdateEntity::update:: {}", entity);
            this.em.merge(entity);
        }
        this.em.flush();

        return entity;
    }

我收到错误:

Caused by: org.hibernate.PersistentObjectException: detached entity passed to persist: de.brockhaus.stock.entity.Stock
at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:124)
at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:765)
at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:758)
at org.hibernate.jpa.event.internal.core.JpaPersistEventListener$1.cascade(JpaPersistEventListener.java:80)
at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:398)
at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:323)
at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:162)
at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:111)
at org.hibernate.event.internal.AbstractSaveEventListener.cascadeBeforeSave(AbstractSaveEventListener.java:425)
at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:249)
at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:178)
at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:121)
at org.hibernate.jpa.event.internal.core.JpaPersistEventListener.saveWithGeneratedId(JpaPersistEventListener.java:67)
at org.hibernate.event.internal.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:189)
at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:132)
at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:58)
at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:775)
at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:748)
at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:753)
at org.hibernate.jpa.spi.AbstractEntityManagerImpl.persist(AbstractEntityManagerImpl.java:1146)
... 138 more

编辑:实现此example ，它使用 @ManyToOne 列注释为 nullable = false，我意识到我的问题与此无关。如之前的服务器日志所示，问题是由 Cascade 类引起的。一些solutions因此建议将 CascadeType.ALL 更改为 CascadeType.MERGE。其他ones展示不同的策略。甚至一些ones告诉只有关联的 OneToMany 端才应该使用级联。坦率地说，我认为在关联双方都使用 CascadeType.ALL 是最好的选择。但看来我错了。虽然，正如我所指出的，我是 JPA 和 Hibernate 的新手，而且我不明白其中的原因。

Answer 1

您可以使用可选标签进行空控制:

@ManyToOne(cascade = CascadeType.ALL, optional = false)
@JoinColumn(name="VENDOR_ID")
private Vendor vendor;