如何在JPQL中使用别名

Question

我正在尝试从H2数据库表中获取一些值。执行我需要的查询是这样的：

SELECT cast(creationDate as date) as DATE, SUM(paymentValue) as TOTAL,fxRate 
FROM payment 
group by DATE

其中“ creationDate”，“ paymentValue”，“ fxRate”是表“
payment”的列。CreationDate是一个时间戳，因此我只需要从中获取日期。当我尝试用Java编写它时

 @Query("SELECT cast(creationDate as date) as daydate , SUM(paymentValue) as value1, fxRate as value2 FROM payment " + 
            "group by cast(creationDate as date)")
    List<Payment> findPaymentValuePerDay ();

我得到了错误 [Ljava.lang.Object; cannot be cast to ...entity.Payment.

我还尝试使用另一个名为GraphDto的对象，该对象的属性为datedate，value1和value2

@Query("SELECT cast(creationDate as date) as daydate , SUM(paymentValue) as value1, fxRate as value2 FROM payment " + 
            "group by cast(creationDate as date)")
    List<GraphDto> findPaymentValuePerDay ();

但我得到同样的错误。

 [Ljava.lang.Object; cannot be cast to ...entity.GraphDto.

因此，如何在JPQL中使用别名？我只需要一个函数，该函数返回3个不同列的名称，并使用正确的H2查询从现有实体获取值。谢谢你们

Answer 1

您的查询返回的是一个Object[]而不是GraphDtoObject 的数组，您可以通过多种方式解决此问题：

解决方案1

创建持有一个构造函数daydate，value1，value2

@Entity
public class GraphDto{

    private Date daydate;
    private Long value1;
    private Long value2;

    public GraphDto(Date daydate, Long value1, Long value2){
        //...
    }
    //..getters and setters
}

那么您的查询应如下所示：

SELECT NEW com.packagename.GraphDto(cast(creationDate AS date), SUM(paymentValue), fxRate)
FROM payment
GROUP BY cast(creationDate AS date)

解决方案2

将返回类型更改为：

List<Object[]> findPaymentValuePerDay ();

然后在服务中遍历此对象并提取值：

List<Object[]> listObject = rep.findPaymentValuePerDay();
for(Object[] obj : listObject){
   Date date = (Date) obj[0];
   Long value1 = (Long) obj[1];
   Long value2 = (Long) obj[2];
}