Ordering by some fields in a table without relationship

Question

Hibernate 3.5 JPA 1.0

The annotation @OrderBy is used only for one to many or many to many relationship on the list-field. But I want it to use for the single table, that should be ordered by some fields in a table. It is possible? Or another solution?

for example:

SELECT * FROM INTERCHANGE_KEYS order by PANEL_OPTION, KEY_NAME

I don't want to write hql for each table.

Answer 1

You can create interface for all common actions that you use on JPA entities. This interface must have two generics. I will give you example for 2 actions (persist and findAll) but all others (merge, delete, find, ...) can be implemented, too. For example:

    public interface JpaDaoBase {
       public void persist(E e);
       public List findAll(String orderProperty, OrderType orderType);
    }

E class should be JPA entity and K represents java type of property used for primary key (Long for example).

And implementation of interface:

public abstract class JpaDaoBaseImpl implements JpaDaoBase {

        protected Class entityClass;

        public JpaDaoBaseImpl() {
            this.entityClass = (Class) ((ParameterizedType) getClass()
            .getGenericSuperclass()).getActualTypeArguments()[0];
        }

        @Override
        public void persist(E e) {
             entityManager.persist(e);
        }

        @Override
        public List findAll(String orderProperty, OrderType orderType) {
        return entityManager.createQuery(
         "select o from " + entityClass.getName() + " o orderby " 
                  orderProperty + + " " + orderType.toString(), entityClass)
         .getResultList();
        }
   }

After that, for entity Example you crate implementation of DAO ExampleDao by extending JpaDaoBaseImpl and you will have this two methods implemented out of the box.

This is a standard way to create DAO layer in JPA (Hiberante) projects. If you use Spring you can use Spring Data JPA project (they have several standard implementations of Dao layer classes).