Hibernate - 使用“非实体类”创建自定义查询结果 [英] Hibernate - createNativeQuery with "non-entity class" result

问题描述

在Hibernate中有没有什么方法可以使用createNativeQuery在查询中选择单个或多个字段而不使用实体类作为返回对象？

我试图在不使用任何XML相关的东西的情况下做到这一点。

  Query query = getEntityManager（）。createNativeQuery（select name from contact where id_contact =：idContact，String.class）; 
 query.setParameter（idContact，9293L）; 
 Object string = query.getSingleResult（）; 
 System.out.println（string）; 
  

使用此函数我有例外：线程mainjavax中的异常。 persistence.PersistenceException：org.hibernate.MappingException：未知实体：java.lang.String

谢谢

编辑：

我也试过：

  Query query = getEntityManager（）。createNativeQuery（select name from contact where id_contact =：idContact）; 
 query.setParameter（idContact，9293L）; 
 List list = query.getResultList（）; 
 if（！list.isEmpty（））{
 Object string = list.get（0）; 
 System.out.println（string）; 
 
 $ / code> 

使用相同的异常：线程中的异常main java.lang.ClassCastException：java.lang.String不能转换为[Ljava.lang.Object;

编辑（2）：
我开始认为这是Hibernate中的一个bug，或者做这种事情是不可能的......

解决方案

问题在于你传递 String.class 作为 createNativeQuery 的第二个参数。这会让休眠尝试使用 String.class 来创建结果集的映射。它只能从实体类创建映射，并且 String 不是实体类，因为它没有映射到表。

$ b $幸运的是，解决方案是简单地使用不需要第二个参数的 createNativeQuery 的重载版本。

  String SQL =..; //与
之前的SQL具有相同的SQL查询query = getEntityManager（）。createNativeQuery（SQL）; //没有实体映射
 query.setParameter（idContact，9293L）; 
 Object string = query.getSingleResult（）; 
 System.out.println（string）; 
  

I'm new to all this Hibernate/JPA stuff, so i will try to be as clear as possible.

Is there any way in Hibernate to use createNativeQuery to select a single/or multiple fields in a query without using an Entity class as the return object ?

I'm trying to do this without using any XML related stuff.

Query query = getEntityManager().createNativeQuery("select name from contact where id_contact = :idContact", String.class);
query.setParameter("idContact", 9293L);
Object string = query.getSingleResult();
System.out.println(string);

Using this i have the Exception : Exception in thread "main" javax.persistence.PersistenceException: org.hibernate.MappingException: Unknown entity: java.lang.String

Thanks

Edit :

I also tried :

Query query = getEntityManager().createNativeQuery("select name from contact where id_contact = :idContact");
query.setParameter("idContact", 9293L);
List list = query.getResultList();
if (!list.isEmpty()){ 
    Object string = list.get(0);
    System.out.println(string);
}

With the same Exception : Exception in thread "main" java.lang.ClassCastException: java.lang.String cannot be cast to [Ljava.lang.Object;

Edit (2) : I'm starting to think it's either a bug in Hibernate or it's impossible to do such things...

解决方案

The problem is that you are passing String.class as the second parameter to createNativeQuery. This will make hibernate attempt to use the String.class to create a mapping for the result set. It can only create this mapping from entity classes and String is not an entity class because it isn't mapped to a table.

Fortunately, the solution is to simply use an overloaded version of createNativeQuery that doesn't require a second parameter.

String SQL = ".."; //same SQL as you had before
Query query = getEntityManager().createNativeQuery(SQL); //no entity mapping
query.setParameter("idContact", 9293L);
Object string = query.getSingleResult();
System.out.println(string);

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