Question

以下从JPA查询获取Spring Data Projection的方法对我来说不起作用：

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

我的表：

LOOKUP_T

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

ACTIVITIES_T（activity_category_id映射到LOOKUP_T.id）

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

Spring Data DAO接口，用于从此连接中获取某些字段：

@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 Data Projection Model接口：

public interface MySpringDataProjection {

    public String getActivityTitle();

    public String getCategory();

    public Integer getCategoryDisplayOrderNum();

}

一切都与接受的答案相同。但得到这个错误：

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(..)，它很脏并且依赖于Hibernate，而我们正在将其抽象为JPA。

我想让这种投影方法起作用。

我引用的（非工作）答案的相关问题， Spring data JPA: getting No aliases found in result tuple! error when executing custom query

Answer 1

我遇到同样的问题。在尝试了几次更改之后，我发现我们只需要在NativeQuery中为每列添加“as”（甚至列名不会更改）。对你来说，改变你的sql：

    @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 ")

Answer 2

我认为你必须在界面中定义确切的名称方法，但我不确定这种方法适用于你的情况。

这里重要的一点是，此处定义的属性与聚合根中的属性完全匹配。这允许像这样添加查询方法

在您的示例中，您可以尝试Open Projection

Answer 3

我有同样的问题，我想我解决了。我所做的是在所有字段中使用别名，即使它们具有相同的名称。在activityTitle中也使用别名。像这样：

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

    @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 ")
    public List<MySpringDataProjection> findCustom();

}

Spring Data Projection和Error：＆＃34;在结果元组中找不到别名！确保您的查询定义了别名！＆＃34;

3 个答案: