java - 无法使用 jpa 更新对象

Question

我在更新记录时遇到问题:

package legacy.database;

import java.sql.Timestamp;
import java.util.ArrayList;
import java.util.List;
import java.util.logging.Logger;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.Query;
import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Predicate;
import javax.persistence.criteria.Root;

public class Queries {

    private static final Logger log = Logger.getLogger(Queries.class.getName());
    private final EntityManagerFactory emf = Persistence.createEntityManagerFactory("LegacyDatabasePU");
    private final EntityManager em = emf.createEntityManager();

    public Queries() {
    }

    private List<Clients> findAll() {
        Query q = em.createQuery("select c from Clients c");
        List<Clients> clients = q.getResultList();
        return clients;
    }




    public Clients findById(int id) {
        Clients client = em.find(Clients.class, id);
        return client;
    }


    public void update(Clients c2) {
        Clients c1 = em.find(Clients.class, c2.getId());
        java.util.Date date = new java.util.Date();
        Timestamp t = new Timestamp(date.getTime());
        c2.setDateUpdated(t.toString());
        em.getTransaction().begin();
        c2.setDateUpdated(t.toString());
        c1 = c2;
        log.info(c1.getNotes());
        log.info(c2.getNotes());
        em.getTransaction().commit();
    }
}

分配c1=c2有问题吗？我是否必须手动检查 c1 并更新每条记录？

Answer 1

在事务中执行 find()，然后在事务中调用您的变异方法。然后提交将自动更新对象。只需简单移动 begin txn 即可实现这一点。只有您知道各种更新是什么，因此不会尝试清理它

try
{
    em.getTransaction().begin();

    Clients c1 = em.find(Clients.class, c2.getId());
    Timestamp t = new Timestamp(new java.util.Date().getTime());
    c2.setDateUpdated(t.toString());
    c1 = c2;
    log.info(c1.getNotes()); log.info(c2.getNotes());

    em.getTransaction().commit();
}
finally
{
    if (em.getTransaction().isActive())
    {
        em.getTransaction().rollback();
    }
}