JPA Query.getResultList() - use in a generic way

Question

I'm creating a complex query with multiple tables and need to list the result. Usually, I'm using the EntityManager and map the result to the JPA-Representation:

UserEntity user = em.find(UserEntity.class, "5"); 

Then I can access all values as the user UserEntity class defines it. But how can I access the field-values returned from a native, multiple-table query? What I get is a List of Objects. That's fine so far, but what "is" that Object? Array? Map? Collection? ...

//simpleExample Query query = em.createNativeQuery("SELECT u.name,s.something FROM user u, someTable s WHERE s.user_id = u.id"); List list = query.getResultList();  //do sth. with the list, for example access "something" for every result row. 

I guess the answer is quite simple, but most examples out there just show the usage when directly casting to a targetClass.

PS: In the example I could use the class-mappings of course. But in my case someTable is not managed by JPA, and therefore I don't have the entity nor do I have a class-representation of it, and since I'm joining like 20 tables, I don't want to create all the classes just to access the values.

Answer 1

General rule is the following:

• If select contains single expression and it's an entity, then result is that entity
• If select contains single expression and it's a primitive, then result is that primitive
• If select contains multiple expressions, then result is Object[] containing the corresponding primitives/entities

So, in your case list is a List<Object[]>.

Answer 2

Since JPA 2.0 a TypedQuery can be used:

TypedQuery<SimpleEntity> q =          em.createQuery("select t from SimpleEntity t", SimpleEntity.class);  List<SimpleEntity> listOfSimpleEntities = q.getResultList(); for (SimpleEntity entity : listOfSimpleEntities) {     // do something useful with entity; }