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javajpaentity

JPA: Result list - Cast Object[] to tuple

simple question, but I don't see my error in reasoning. Having a named query with selected members as result instead of the entire row/entity.

Now I want to access the member fields with the convenient tuple methods.

q = em.createNamedQuery("test.findvar");
List<Tuple> tuples = q.getResultList();    
for (Tuple t : tuples)
   System.out.println(t.get(0) + " " + t.get(1));

Unfortunately it throws me:

Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to javax.persistence.Tuple

All works fine with:

q = em.createNamedQuery("test.findvar");
List<Object[]> objs = q.getResultList();    
for (Object[] obj : objs)
    System.out.println(obj[0] + " " + obj[1]);

What's wrong with my first solution?

Solution

  • You can specify return type in createNamedQuery(), as noted in javadoc

    So your code should look like:

    q = em.createNamedQuery("test.findvar", Tuple.class);
List<Tuple> tuples = q.getResultList();    
for (Tuple t : tuples)
   System.out.println(t.get(0) + " " + t.get(1));

    When you specify return type, TypedQuery instance is created, instead of Query instance. Query does not use generics and returns simply java.util.List.