java - Hibernate EntityManager 不会在持久化时抛出 EntityExistsException

Question

我对 Hibernate EntityManager 有疑问。

这是我的 DAO 函数:

public Boolean create(T element)
{
    System.out.println("To persist: "+element);
    System.out.println("PersistanceHolder: "+holder);
    System.out.println("EntityManager: "+entityManager);
    System.out.println("CRUDDao: "+this);
    System.out.println("Thread: "+Thread.currentThread());

    entityManager.getTransaction().begin();

    try
    {
        entityManager.persist(element);
    }
    catch(EntityExistsException e)
    {
        entityManager.getTransaction().rollback();
        return Boolean.FALSE;
    }

    entityManager.getTransaction().commit();

    return Boolean.TRUE;
}

我的元素是这样的:

@Entity
public class Event {

    @Id
    String name;

    Maturity maturity;

    Integer delay;

    public Event() {
    }

    public Event(String name, Maturity maturity, Integer delay) {
        super();
        this.name = name;
        this.maturity = maturity;
        this.delay = delay;
    }

    public String getName() {
        return name;
    }
    public Maturity getMaturity() {
        return maturity;
    }
    public Integer getDelay() {
        return delay;
    }

    @Override
    public String toString() {
        return "Event [name=" + name + ", maturity=" + maturity + ", delay="
                + delay + ", toString()=" + super.toString() + "]";
    }
}

数据库中的元素如下所示:

Added: Event [name=Mercury, maturity=monthEnd, delay=0, toString()=bc.bacon.egg.data.local.pojos.events.Event@3b43dc25]

如果我现在插入一个索引(名称)已经存在的元素，我会收到此消息:

To persist: Event [name=Mercury, maturity=monthEnd, delay=0, toString()=bc.bacon.egg.data.local.pojos.events.Event@7025bd08]
PersistanceHolder: bc.bacon.egg.data.local.PersistanceHolder@3d9d91bd
EntityManager: org.hibernate.jpa.internal.EntityManagerImpl@33cb2ee5
CRUDDao: bc.bacon.egg.data.local.dao.events.EventsDao@6073d6f3
Thread: Thread[qtp1055127737-17,5,main]

因此抛出 EntityExistsException 并且一切正常。
但是在第二次运行时我得到了这个:

To persist: Event [name=Mercury, maturity=monthEnd, delay=0, toString()=bc.bacon.egg.data.local.pojos.events.Event@700576a4]
PersistanceHolder: bc.bacon.egg.data.local.PersistanceHolder@3d9d91bd
EntityManager: org.hibernate.jpa.internal.EntityManagerImpl@33cb2ee5
CRUDDao: bc.bacon.egg.data.local.dao.events.EventsDao@6073d6f3
Thread: Thread[qtp1055127737-16,5,main]
Hibernate: insert into Event (delay, maturity, name) values (?, ?, ?)
Jun 18, 2015 3:10:34 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExceptions
WARN: SQL Error: 23505, SQLState: 23505
Jun 18, 2015 3:10:34 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExceptions
ERROR: Eindeutiger Index oder Primärschlüssel verletzt: "PRIMARY_KEY_3 ON PUBLIC.EVENT(NAME) VALUES ('Mercury', 1)"
Unique index or primary key violation: "PRIMARY_KEY_3 ON PUBLIC.EVENT(NAME) VALUES ('Mercury', 1)"; SQL statement:
insert into Event (delay, maturity, name) values (?, ?, ?) [23505-187]
Jun 18, 2015 3:10:34 PM org.hibernate.engine.jdbc.batch.internal.AbstractBatchImpl release
INFO: HHH000010: On release of batch it still contained JDBC statements
Jun 18, 2015 3:10:34 PM com.vaadin.server.DefaultErrorHandler doDefault

现在我的问题是，为什么第一次调用没问题并且找到了重复项，但在第二次运行时却不行？好的，我可以捕获在 commit() 函数中抛出的异常，但是，我如何才能删除剩余的 JDBC 语句？

谢谢，乔希

Answer 1

您应该只为 NEW/TRANSIENT 中的实体调用持久化状态。因为您要起诉分配的标识符，所以最好改用合并(因为 Hibernate 无法确定提供的实体是新实体还是分离实体)。

所以代替:

entityManager.persist(element);

使用这个:

entityManager.merge(element);