Spring数据投影和错误：“在结果元组中没有找到别名！确保您的查询定义了别名！”

Question

下面从JPA查询中获取Spring数据投影的方法对我不起作用：

https://stackoverflow.com/a/45443776/1005607

id   description    display_order_num
------------------------------------
1    Category #1    1
2    Category #2    2

id  activity_category_id  activity_title
---------------------------------------
1      2                  Sleeping
2      2                  Eating
3      2                  Travel

@Repository
public interface ActivitiesDAO extends JpaRepository<ActivitiesT, Integer> {

    @Query("select a.activityTitle, l.description as category, " + 
           "l.displayOrderNum as categoryDisplayOrderNum " + 
           "from ActivitiesT a, LookupT l " + 
           "where a.lookupT.id = l.id order by l.displayOrderNum asc ")
    public List<MySpringDataProjection> findCustom();

}

Spring数据投影模型界面：

public interface MySpringDataProjection {

    public String getActivityTitle();

    public String getCategory();

    public Integer getCategoryDisplayOrderNum();

}

一切都和那个公认的答案一样。但是得到这个错误：

org.springframework.dao.InvalidDataAccessApiUsageException: No aliases found in result tuple! Make sure your query defines aliases!; nested exception is java.lang.IllegalStateException: No aliases found in result tuple! Make sure your query defines aliases!
    org.springframework.orm.jpa.EntityManagerFactoryUtils.convertJpaAccessExceptionIfPossible(EntityManagerFactoryUtils.java:381)
    org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.translateExceptionIfPossible(AbstractEntityManagerFactoryBean.java:489)
    org.springframework.dao.support.ChainedPersistenceExceptionTranslator.translateExceptionIfPossible(ChainedPersistenceExceptionTranslator.java:59)
    org.springframework.dao.support.DataAccessUtils.translateIfNecessary(DataAccessUtils.java:213)

我不想在查询中使用select new Obj(..)，它很脏，依赖于我们将其抽象为JPA的Hibernate。

Answer 1

我遇到同样的问题。在尝试了几个更改之后，我发现我们只需要为NativeQuery中的每个列添加“as”（即使列名也没有更改）。对于这里的您，更改您的sql，如下所示：

    @Query("select a.activityTitle **as activityTitle**, l.description as category, " + 
       "l.displayOrderNum as categoryDisplayOrderNum " + 
       "from ActivitiesT a, LookupT l " + 
       "where a.lookupT.id = l.id order by l.displayOrderNum asc ")