如何在 JPQL 中使用别名

Question

我正在尝试从 H2 db 表中获取一些值。做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“payment”表的列。CreationDate 是一个时间戳，所以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 ();

我收到错误 [Ljava.lang.Object; cannot be cast to ...entity.Payment.

我还尝试使用一个名为 GraphDto 的不同对象，它具有属性 daydate、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 ();

但我得到了同样的错误。

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

那么，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，其中的值使用正确的 H2 查询从现有实体中获取。谢谢你们

Answer 1

您的查询返回一个数组Object[]而不是GraphDtoObject，您有多种方法可以解决此问题：

解决方案1

创建一个构造函数，其中包含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 ();

然后在您的服务循环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];
}