如何返回特定类型的列表而不是 List<Object[]>在休眠中? [英] How to return a list of specific type instead of List&lt;Object[]&gt; in Hibernate?

问题描述

我有类树:

classA {B级；C级；.....}

我有这样的 HQL 查询:

SELECT a.field1, b.field2, c.field3, c.field4从左外连接 b 上 a.id = b.fk左外连接 c on b.id = c.fk

此查询返回List.

是否可以将返回的数据转换为以下类:

classD {类型 1 字段 1；类型 2 字段 2；Type3 field3;}

那么可以通过 Hibernate 进行投射还是我需要手动进行所有投射?

解决方案

JPA 查询中有不同类型的选择.您当前使用的是 Array 作为返回类型，您需要的是 Construct 返回类型. 这是如何实现的:

String queryStr =选择新的包.YourDefinedCustomClass(a.field1, b.field2, c.field3, c.field4) 来自左外连接 b在 a.id=b.fk 上左外连接 c 在 b.id=c.fk 上";TypedQuery查询 =em.createQuery(queryStr, YourDefinedCustomClass.class);List结果 = query.getResultList();

基本上有两件事:

1. 自定义类必须是您的结果返回类型
2. 自定义类必须有一个构造函数，它接受您在查询字符串中定义的结果值.

阅读有关 JPA2 查询中选择的更多信息.>

I have tree of classes:

classA {  
      classB b;  
      classC c;
      .....
} 

I have HQL query like this:

SELECT a.field1, b.field2, c.field3, c.field4
FROM a LEFT OUTER JOIN b ON a.id = b.fk
       LEFT OUTER JOIN c ON b.id = c.fk 

This query returns List<Object[]>.

Is it possible to cast the returned data to the following class:

classD {
    Type1 fiedl1;
    Type2 field2;
    Type3 field3;
}

So can casting be made by Hibernate or I need manually do all casting?

解决方案

There are different types of selects in JPA queries. You are currently using Array as a return type, what you need is Construct return type. Here is how to achieve this:

String queryStr =
    "select NEW package.YourDefinedCustomClass(
     a.field1, b.field2, c.field3, c.field4) from a left outer join b 
     on a.id=b.fk left outer join c on b.id=c.fk";

TypedQuery<YourDefinedCustomClass> query =
    em.createQuery(queryStr, YourDefinedCustomClass.class);

List<YourDefinedCustomClass> results = query.getResultList();

Basically there are two things:

1. Custom class must be your results return type
2. Custom class must have a constructor which takes result values you define in query string.

Read more on selects in JPA2 queries.

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