EclipseLink error: Exception Description: Missing descriptor for class

Question

I just want to make a simple native query with EclipseLink, but I can't make it work

    @Repository("CarsRepository")
public class JpaCarsRepository {

    @PersistenceContext 
    private EntityManager em;

    public List<Car> getCars(){
     Query q=em.createNativeQuery("SELECT id,name_car FROM CARS",Car.class);
     List<Car> results=q.getResultList();

My 'Car' class is defined as an @Entity. (my persistence.xml has just the basic connection settings) I get a 'Missing descriptor' error for class 'Car'.

Why is this happening? I saw a similar question which didn't help me.

2nd question:

If I don't specify the 2nd parameter of 'createNativeQuery' function (Car.class), it returns a list of Objects, so I can see results.get(0) value is [1 car]. I can iterate over the list of objects. So if

Object o=results.get(0)

I could create the Car objects manually, but I don't know how to get first value of the object, if I print o[0] to get value 1 of the object (which is [1 car]) I get the following error the type of expression must be array type but resolved to object

How could I access to each value of the object?

Solution

It does not consider Car as entity, looks like it is not scanned. Does listing your entity inside class-element in persistence.xml help?

Your second attempt returns list of object arrays. To access values you have to first cast to the one row of result set to Object array:

Object[] o=results.get(0)
//types below are just guessed:
Integer id = o[0];
String name = o[1];

Comments

[de3]

I added previosuly my entity in persistence.xml with no success, but after trying again I found out my error was not specifying @Id, and @Column(name="columname") in my Car model class' properties