hibernate - 如何在每次选择之前阻止 JPA 实体管理器刷新

Question

我在 Spring 使用 JPA(以 hibernate 作为提供者)作为 Web 应用程序。
我有一些方法可以构造要传递给 UI 的复杂对象。作为这些方法流程的一部分，一些 select执行 SQL 语句。问题是实体管理器在每次选择之前刷新，这个 Action 需要很多时间并且阻碍了性能。有没有办法防止实体管理器在每次选择之前刷新？ (我不关心上面选择中的陈旧数据)

谢谢你。

这是我的 GenericDAO

@Repository
public abstract class GenericDAOWithJPA<T, ID extends Serializable> implements IGenericDAO<T, ID> {
    private static final int MAX_RETRIES = 3;
    private static final long WAIT_INTERVAL_MS = 1000;
    static final Logger LOG = LoggerFactory.getLogger(GenericDAOWithJPA.class);

    private Class<T> persistentClass;

    protected EntityManager entityManager;

    @SuppressWarnings("unchecked")
    public GenericDAOWithJPA() {
            this.persistentClass = (Class<T>) ((ParameterizedType) getClass().getGenericSuperclass()).getActualTypeArguments()[0];
    }


    @Override
    @PersistenceContext
    public void setEntityManager(EntityManager entityManager) {
        this.entityManager = entityManager;
        this.entityManager.setFlushMode(FlushModeType.COMMIT)
    }


    @Override
    public Class<T> getPersistentClass() {
        return persistentClass;
    }

    /* (non-Javadoc)
     * @see com.legolas.dao.IGenericDAO#find(ID)
     */
    @Override
    public T find(ID id) {
        return entityManager.find(persistentClass, id);
    }


    @Override
    public T getReference(ID id) {
        return entityManager.getReference(persistentClass, id);
    }

    /* (non-Javadoc)
     * @see com.legolas.dao.IGenericDAO#persist(T)
     */
    @Override
    public void persist(T entity) {
        entityManager.persist(entity);
    }

    @Override
    public void persist(List<T> entityList) {
        for (T entity : entityList) {
            persist(entity);
        }
    }



    @Override
    public T merge(T entity) {
        return entityManager.merge(entity);
    }


    @Override
    public void remove(T entity) {
        entityManager.remove(entity);
    }


    @Override
    @SuppressWarnings("unchecked")
    public List<T> findAll() {
        return entityManager.createQuery("Select t from " + persistentClass.getSimpleName() + " t").getResultList();
    }


    @Override
    @SuppressWarnings("unchecked")
    public List<T> findInRange(int firstResult, int maxResults) {
        return entityManager.createQuery("Select t from " + persistentClass.getSimpleName() + " t").setFirstResult(firstResult).setMaxResults(maxResults).getResultList();
    }


    @Override
    public long count() {
        return (Long) entityManager.createQuery("Select count(t) from " + persistentClass.getSimpleName() + " t").getSingleResult();
    }

    @Override
    public void flush() {
        this.entityManager.flush();
    }

    @Override
    public void refresh(T entity) {
        int retry = 0;
        RuntimeException lastException = null;
        do {
        try {
            this.entityManager.refresh(entity);
        } catch (OptimisticLockException e) {
            retry++;
            lastException = e;
            LOG.debug("OptimisticLockException retry {}", retry);
            try {
                Thread.sleep(WAIT_INTERVAL_MS);
            } catch (InterruptedException e1) {
                retry = MAX_RETRIES;
            }
        }
        } while (lastException != null && retry < MAX_RETRIES);

    }
}

Answer 1

以下代码在查询之前禁用刷新(刷新仅在提交之前发生):

em.setFlushMode(FlushModeType.COMMIT);