JPA - Refresh detatched entity before setting values and persisting

Question

I have an detatched entity and want to set some values. But before that I want to refresh the entity to be sure to have the latest data from the database. I came up with this code. It merges and refreshes my entity before setting some new values.

The problem is, that this creates a new object. Is there a better and simpler way to archieve this?

@Entity
public class MyEntity{


    public void setValueAndPersist(){

        EntityManager em = ...

        em.getTransaction().begin();

        MyEntity newEntity = em.merge(this);

        em.refresh(newEntity);

        newEntity.setSomeVal("someVal");

        em.commit();
    }
}

Answer 1

Use a own class for interaction with database. DONT do this in the entity itself!

Solution1: You can use @Version for current object. https://weblogs.java.net/blog/2009/07/30/jpa-20-concurrency-and-locking . You get a Exception when its not the newest version and you tried to merge it.

Solution2: You can use find(...) http://docs.oracle.com/javaee/6/api/javax/persistence/EntityManager.html#find%28java.lang.Class,%20java.lang.Object%29

With class and ID from the current Item to load the actual state from DB (or Persistence Context if already exists in it).