当 id（主键）大于 1 时，如何获得 EntityManager.getReference？

Question

伙计们，我非常想知道如何将 EntityManager.getReference 与超过 1 个主键一起使用，因为当我想更新数据时总是出错，错误消息有点像：

[EL Fine]: sql: Connection(1713950866)--SELECT Category, SubCategory, Code, CreatedBy, CreatedDateTime, IsActive, Remarks, UpdatedBy, UpdatedDateTime, Value FROM master.sysParameter WHERE (((Category = ?) AND (SubCategory = ?)) AND (Code = ?)) bind => [acm, acm, acm] javax.persistence.EntityNotFoundException: Could not find entity for id: acm at org.eclipse.persistence.internal.jpa.EntityManagerImpl.getReference(EntityManagerImpl.java:1398)

在我的代码中，我想定义 3 个变量，但我只得到 1 个 (acm)。这是我的代码示例：

    public boolean updateSysParameter(MasterSysParameterEntity masterSysParameter) {
    // TODO Auto-generated method stub
    boolean retVal = false;
    try{
        MasterSysParameterEntity updateSysParameter;
        em = getEntityManagerFactory();
        em.getTransaction().begin();
        System.out.println("masterSysParameter.getCategory() => " +masterSysParameter.getCategory());

        updateSysParameter = em.getReference(MasterSysParameterEntity.class, masterSysParameter.getCategory());
        updateSysParameter = em.getReference(MasterSysParameterEntity.class, masterSysParameter.getSubCategory());
        updateSysParameter = em.getReference(MasterSysParameterEntity.class, masterSysParameter.getCode());

        updateSysParameter = em.merge(masterSysParameter);

        em.getTransaction().commit();
        retVal = true;
    }catch (Exception e) {
        if(em != null && null != em.getTransaction())
            em.getTransaction().rollback();
        e.printStackTrace();
    } finally {
        if (em != null) {
            em.close();
        }
    }
    return retVal;
}

非常感谢您的建议和帮助，这真的很重要

Answer 1

当您在一个实体中有多个 @Id 字段时，您可以定义一个 @IdClass on the entity for the composite id。因此，您调用 em.getReference 将第二个参数作为 "IdClass".

的实例传递

MyIdClass myId = new MyIdClass(...); // Pass in whatever args your IdClass needs
MyEntity ent = em.getReference(MyEntity.class, myId);

当 id（主键）大于 1 时，如何获得 EntityManager.getReference？

How can I get EntityManager.getReference when the id(primay keys) are more than 1?

java

jpa

entitymanager

zk