带有 HQL 的新对象 [英] New object with HQL

问题描述

尝试从 HQL 查询创建对象，但无法弄清楚我做错了什么.

Trying to create an object from an HQL query, but just can't figure out what i'm doing wrong.

查询:

String query = "SELECT product.code, SUM(product.price), COUNT(product.code)
from Product AS product
GROUP BY product.code"

(或者我应该使用 new MyCustomList(product.code, SUM(... ，即使它没有被映射?)现在我想把这个返回的列表转换成一个类似的对象:

(or should I use new MyCustomList(product.code, SUM(... , even though it's not mapped?) Now I want to cast this returned list into a similar object:

class MyCustomList{
  public String code;
  public BigDecimal price;
  public int total;

  // Constructor
  public MyCustomList(String code, String price, int total){ //...

检索数据:

// This throws ClassCastException    
List<MyCustomList> list = MyClass.find(query).fetch();

使用 Play 框架

推荐答案

我认为 15.6.select 子句涵盖了您要实现的目标:

I think that the section 15.6. The select clause covers what you're trying to achieve:

...

查询可以返回多个对象和/或属性作为类型数组对象[]:

Queries can return multiple objects and/or properties as an array of type Object[]:

select mother, offspr, mate.name
from DomesticCat as mother
    inner join mother.mate as mate
    left outer join mother.kittens as offspr

或者作为List:

select new list(mother, offspr, mate.name)
from DomesticCat as mother
    inner join mother.mate as mate
    left outer join mother.kittens as offspr

或者——假设类Family有一个合适的构造函数 - 作为实际的类型安全 Java 对象:

Or - assuming that the class Family has an appropriate constructor - as an actual typesafe Java object:

select new Family(mother, mate, offspr)
from DomesticCat as mother
    join mother.mate as mate
    left join mother.kittens as offspr

就您而言，您可能想要:

In your case, you probably want:

SELECT new MyCustomList(product.code, SUM(product.price), COUNT(product.code))
from Product AS product
GROUP BY product.code

其中 MyCustomList 不一定是映射实体.

Where MyCustomList is not necessarily a mapped entity.

这篇关于带有 HQL 的新对象的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！