java 使用 JPA 选择非实体？
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Select non-entities with JPA?
提问by Redfield
Is it possible with JPA to retrieve a instances of a non-entity classes with native queries?
I have a non-entity class that wraps two entities:
JPA 是否可以使用本机查询检索非实体类的实例？
我有一个包装两个实体的非实体类：
class Wrap{
Entity1 ent1;
Entity2 ent2
}
@Entity
class Entity1{
...
}
@Entity
class Entity2{
...
}
How can I do something like that?
我怎么能做这样的事情？
Query q = entityManager.createNativeQuery("native select here");
List<Wrap> list = q.getResultList();
回答by Pascal Thivent
Is it possible with JPA to retrieve a instances of a non-entity classes with native queries?
JPA 是否可以使用本机查询检索非实体类的实例？
No. Native queries can return entities only(if you tell them to do so by passing the resultClassor a resultSetMappingto the createNativeQuerymethod; if you don't, you will get collections of raw data).
号机查询可以返回实体只（如果你告诉他们通过将这样做，resultClass或者resultSetMapping给createNativeQuery方法;如果你不这样做，你会得到原始数据的集合）。
In JPQL, you can use constructor expressions (SELECT NEW...) whith a non-entity constructor. But this is not supported for native queries, you'll have to do it manually.
在 JPQL 中，您可以使用带有非实体构造函数的构造函数表达式 (SELECT NEW...)。但是本机查询不支持此操作，您必须手动执行此操作。
回答by Lakshmi Hari
I think I found the solution. There is a way to use the NEW keyword in constructing the query. What I did to resovle this issue :
我想我找到了解决方案。有一种方法可以在构造查询时使用 NEW 关键字。我做了什么来解决这个问题：
public List<ProductType> getProductByName(String productName) {
String sqlQuery = "select DISTINCT **NEW** project1.ProductType(o.name, o.revision) from Lhproduct o where o.name = :prodname";
Query qry = getEntityManager().**createQuery(sqlQuery);**
qry.setParameter("prodname",productName);
return qry.getResultList();
}
The ProductType is a non-entity object, a simple plain object implementing Serialiabale. But you need to define the appropriate constructor.
ProductType 是一个非实体对象，一个简单的实现了Serialiabale 的普通对象。但是您需要定义适当的构造函数。
Happy coding :-)
快乐编码:-)
Thanks and Regards, Hari
谢谢和问候，哈里
