I am trying to run this basic JPA/EJB code:

public static void main(String[] args){
         UserBean user = new UserBean();
         user.setId(1);
         user.setUserName("name1");
         user.setPassword("passwd1");
         em.persist(user);
  }

I get this error:

javax.ejb.EJBException: javax.persistence.PersistenceException: org.hibernate.PersistentObjectException: detached entity passed to persist: com.JPA.Database

Any ideas?

I search on the internet and the reason I found was:

This was caused by how you created the objects, i.e. If you set the ID property explicitly. Removing ID assignment fixed it.

But I didn't get it, what will I have to modify to get the code working?