无法使用请求结果类型为具有多个返回的查询创建类型查询 [英] Cannot create Typed Query for query with more than one return using request result type

问题描述

我正在尝试将oracle结果列表绑定到摘要列表.但是我的 summary 列表中有3个类定义为DB实体

I'm trying to bind oracle result list to a summary list. But my summary list has 3 classes defined as entities of DB

我有三个实体类别A，B，C

I have three entity classes A, B, C

Summary.class
{
    @Autowired
    private A a;

    @Autowired
    private B b;

    @Autowired
    private C c;

    //getters and setters
}

@Enity
class A{
Fields 1..n ;
}  // same goes for other classes definition

我通过以下查询获得结果，但结果无法转换为摘要对象

I get the results with following query, but the results cannot be cast to the Summary object

List<Summary> summaryList = entityManager.createQuery("from A a, B b, C c" +
                " where a.field1 = b.field1 and a.fValue = :fValue " +
                "and b.field3= c.field3", Summary.class)
                .setParameter("fValue ", fValue )
                .getResultList();

调试: 我确保结果列表不为空，并且如果不将其强制转换为对象，则在下面的查询中可以正常工作

Debugging: I made sure resultslist is not empty and below query works fine if I dont cast it to an object

List summaryList = entityManager.createQuery("from A a, B b, C c" +
                    " where a.field1 = b.field1 and a.fValue = :fValue " +
                    "and b.field3= c.field3")
                    .setParameter("fValue ", fValue )
                    .getResultList();

我看到的替代方法1是遍历summaryList并将其分配给这样的单个列表，我尚未对其进行测试，但是我认为它可能会产生类强制转换异常，因为之前强制执行dint工作

The alternative 1 I see is to iterate through summaryList and assign it them to individual lists like this, which I haven't tested yet but I think it might give a class cast exception since the casting dint work before

for (int i = 0; i < summaryList.size(); i++) {
   Summary s= (Summary) summaryList.get(i); // might be class cast Exception
   aList.add(s.getA());
   bList.add(s.getB());
}

我在想的替代方案2是 从db获得唯一的A类字段列表，将其转换为A的列表，执行3次蛮力直到我全部获得.

The alternative 2 I'm thinking is to get only class A fields list from db cast it to A's List, do it 3 times brute force till I get all of them.

下面是我在创建新问题之前先看过的一些问题

Below are some of questions I looked at before creating a new question

使用不同的类来组合多个实体类

获取列表回映射到pojo

请让我知道您的想法，我认为我的主要方法是行之有效的好方法.

Please let me know your thoughts, I'm thinking my main approach is good way to do it if it works.

推荐答案

您的JPQL选择语句"from A a, B b, C c"无法映射回Summary实体，JPA没有足够的信息来做到这一点.

Your JPQL select statement "from A a, B b, C c" can not be mapped back to Summary entity, JPA does not have enough info to do that.

如果按照您的逻辑，可以由A，B，C组成一个摘要实例，那么您可以使用类似
的构造函数

If in your logic, a summary instance can be composed from A, B, C then you can have a constructor like

public Summary(A a, B b, C c) {
       .............
}

并将您的选择陈述更改为

and changed your select statment to be

"select new Summary(a, b, c) FROM A a, B b, C c"

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