Java Hibernate - createNativeQuery 与“非实体类”结果
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Hibernate - createNativeQuery with "non-entity class" result
提问by Joshua
I'm new to all this Hibernate/JPA stuff, so i will try to be as clear as possible.
我对所有这些 Hibernate/JPA 东西都不熟悉，所以我会尽量说清楚。
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 ?
在 Hibernate 中是否有任何方法可以使用 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？
I'm trying to do this without using any XML related stuff.
我试图在不使用任何与 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);
Using this i have the Exception : Exception in thread "main" javax.persistence.PersistenceException: org.hibernate.MappingException: Unknown entity: java.lang.String
使用这个我有例外： Exception in thread "main" javax.persistence.PersistenceException: org.hibernate.MappingException: Unknown entity: java.lang.String
Thanks
谢谢
Edit :
编辑 ：
I also tried :
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);
}
With the same Exception : Exception in thread "main" java.lang.ClassCastException: java.lang.String cannot be cast to [Ljava.lang.Object;
同样的例外： 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...
编辑（2）：我开始认为这要么是 Hibernate 中的错误，要么是不可能做这样的事情......
回答by Adam Dyga
Just try to call createNativeQuery()without passing String.class. If the namecolumn is of string-type in database query.getSingleResult()will actually return a String.
只是尝试调用createNativeQuery()而不通过String.class。如果name数据库中的列是字符串类型，query.getSingleResult()实际上将返回一个String.
回答by cyon
The problem is that you are passing String.classas the second parameter to createNativeQuery. This will make hibernate attempt to use the String.classto create a mapping for the result set. It can only create this mapping from entity classes and Stringis not an entity class because it isn't mapped to a table.
问题是您String.class作为第二个参数传递给createNativeQuery. 这将使 hibernate 尝试使用String.class为结果集创建映射。它只能从实体类创建此映射，并且String不是实体类，因为它没有映射到表。
Fortunately, the solution is to simply use an overloaded version of createNativeQuerythat doesn't require a second parameter.
幸运的是，解决方案是简单地使用createNativeQuery不需要第二个参数的重载版本。
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);
回答by sunysen
try
尝试
Query query = getEntityManager().createNativeQuery("select name from contact where id_contact = :idContact", String.class);
query.setParameter("idContact", 9293L);
List list = query.getResultList();
if (!list.isEmpty()){
Object string = list.get(0);
System.out.println(string);
}
In the Look here
在看这里
http://sysout.be/2011/03/09/why-you-should-never-use-getsingleresult-in-jpa
http://sysout.be/2011/03/09/why-you-should-never-use-getsingleresult-in-jpa
回答by AjGupta
In case of Native query or jpql with column name EntityManager Returns a List of array of objects.
在本机查询或列名 jpql 的情况下，EntityManager 返回对象数组列表。
so to get Result List.
所以得到结果列表。
receive it in a
接收它
List<Object[]> listResults = query.getResultList();
then iterate over it:-
然后迭代它：-
for (Object[] record : listResults) {
//Iterate Logic will come here
}
回答by user7990606
String SQL = ".."; //same SQL as you had before
Query query = getEntityManager().createNativeQuery(SQL); //no entity mapping
query.setParameter("idContact", 9293L);
String string = (String)query.getSingleResult();
System.out.println(string);
回答by karepu
For Hibernate 5.0
对于休眠 5.0
Query query = getEntityManager().createNativeQuery(sql);
List<Object[]> objects = query.getResultList();
System.out.println(objects.get(0)[0]);
https://docs.jboss.org/hibernate/orm/5.0/userguide/html_single/chapters/query/native/Native.html
https://docs.jboss.org/hibernate/orm/5.0/userguide/html_single/chapters/query/native/Native.html
