JPA查询可以将结果作为Java Map返回吗? [英] Can a JPA Query return results as a Java Map?

问题描述

我们当前正在基于命名的JPA查询返回的两个字段手动构建Map，因为JPA 2.1仅提供了getResultList()方法:

We are currently building a Map manually based on the two fields that are returned by a named JPA query because JPA 2.1 only provides a getResultList() method:

@NamedQuery{name="myQuery",query="select c.name, c.number from Client c"}

HashMap<Long,String> myMap = new HashMap<Long,String>();

for(Client c: em.createNamedQuery("myQuery").getResultList() ){
     myMap.put(c.getNumber, c.getName);
}

但是，我觉得自定义映射器或类似的映射器会更有效，因为此列表可以轻松获得30,000多个结果.

But, I feel like a custom mapper or similar would be more performant since this list could easily be 30,000+ results.

任何无需手动迭代即可构建Map的想法.

Any ideas to build a Map without iterating manually.

(我正在使用OpenJPA，而不是休眠状态)

(I am using OpenJPA, not hibernate)

推荐答案

没有标准方法让JPA返回地图.

There is no standard way to get JPA to return a map.

请参阅相关问题: JPA 2.0本机查询结果作为地图

手动迭代应该没问题.相对于执行/返回查询结果的时间，在内存中迭代列表/映射的时间将很小.除非有确凿的证据表明手动迭代不可行，否则我不会尝试使用JPA内部或自定义功能.

Iterating manually should be fine. The time to iterate a list/map in memory is going to be small relative to the time to execute/return the query results. I wouldn't try to futz with the JPA internals or customization unless there was conclusive evidence that manual iteration was not workable.

此外，如果您在其他地方将查询结果列表转换为地图，则可能希望将其重构为带有参数的实用程序方法，以指示地图键属性.

Also, if you have other places where you turn query result Lists into Maps, you probably want to refactor that into a utility method with a parameter to indicate the map key property.

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