JPA - EntityManager.getReference Examples

    private static void loadEntity(EntityManagerFactory emf) {
        System.out.println("-- loading employee by id --");
        EntityManager em = emf.createEntityManager();
        System.out.println("calling getReference().");
        Employee employee = em.getReference(Employee.class, 1);
        System.out.println("getReference() already called");
        System.out.println("loaded employee name: " + employee.getName());
        em.close();
    }

    private static Employee getEntityReference(EntityManagerFactory emf) {
        EntityManager em = emf.createEntityManager();
        Employee employee = em.getReference(Employee.class, 1);
        em.close();
        return employee;
    }

    private static void updateByReference(EntityManagerFactory emf) {
        System.out.println("-- updating employee by reference --");
        EntityManager em = emf.createEntityManager();
        Employee employee = em.getReference(Employee.class, 1);
        em.getTransaction().begin();
        System.out.println("-- setting new department --");
        employee.setDepartment("IT");
        System.out.println("-- commit --");
        em.getTransaction().commit();
        em.close();
    }

    private static void persistEmployee(EntityManagerFactory emf) {
        System.out.println("-- persisting employee --");
        Employee employee = new Employee();
        employee.setName("Joe");
        EntityManager em = emf.createEntityManager();
        Task task = em.getReference(Task.class, 1);
        employee.setTask(task);
        em.getTransaction().begin();
        em.persist(employee);
        em.getTransaction().commit();
        em.close();
        System.out.println("Employee persisted: " + employee);
    }

    private static void persistEmployees(EntityManagerFactory emf) {
        System.out.println("-- persisting employees --");

        EntityManager em = emf.createEntityManager();
        Department department = em.getReference(Department.class, 1);

        Employee employee1 = new Employee();
        employee1.setName("Joe");
        employee1.setDepartment(department);

        Employee employee2 = new Employee();
        employee2.setName("Jackie");
        employee2.setDepartment(department);

        em.getTransaction().begin();
        em.persist(employee1);
        em.persist(employee2);
        em.getTransaction().commit();
        em.close();
        System.out.println("Employee persisted: " + employee1);
        System.out.println("Employee persisted: " + employee2);
    }

    private static void findByGetReference() {
        EntityManager em = entityManagerFactory.createEntityManager();
        Employee employee = em.getReference(Employee.class, 1);
        System.out.println("after find(): " + em.contains(employee));
        em.close();
    }

    private static void findByReferenceAndRemoveEntity() {
        EntityManager em = entityManagerFactory.createEntityManager();
        Employee employee = em.getReference(Employee.class, 1);
        System.out.println("after getReference(): " + em.contains(employee));
        em.remove(employee);
        System.out.println("after remove(): " + em.contains(employee));
        em.close();
    }

    private static void findByReferenceAndDetachEntity() {
        EntityManager em = entityManagerFactory.createEntityManager();
        Employee employee = em.getReference(Employee.class, 1);
        System.out.println("after getReference(): " + em.contains(employee));
        em.detach(employee);
        System.out.println("after detach(): " + em.contains(employee));
        em.close();
    }

    private static void findByRefDetachAndMerge() {
        EntityManager em = entityManagerFactory.createEntityManager();
        Employee employee = em.getReference(Employee.class, 1);
        System.out.println("after getReference(): " + em.contains(employee));
        em.detach(employee);
        System.out.println("after detach(): " + em.contains(employee));
        employee = em.merge(employee);
        System.out.println("after merge(): " + em.contains(employee));
        em.close();
    }