JPA使用IdClass問題刪除查詢

Question

當我在JPA中使用Idclass用於具有復合鍵的實體時，我編寫了一個remove方法，如：

private static void removeEmployee(Employee employee) {
    EntityManagerFactory emf = Persistence
            .createEntityManagerFactory("JPA_excer_3b");
    EntityManager em = emf.createEntityManager();
    try {
        em.getTransaction().begin();
        Employee anemployee = em.find(Employee.class, employee.getId());
        em.remove(anemployee);
        em.getTransaction().commit();
    } catch (Exception e) {
        logging.error("This error is added a removing a employee :"
                + " :" + e);
    } finally {
        // Close all the connections:
        em.close();
        emf.close();
    }
}

我收到錯誤：

ERROR Logger:22 - This error is added a removing a employee :java.lang.IllegalArgumentException: Provided id of the wrong type for class be.leerstad.JPA.entities.Employee. Expected: class be.leerstad.JPA.entities.EmployeePK, got class java.lang.Integer

當我將代碼更改為：

private static void removeEmployee(Employee employee) {
    EntityManagerFactory emf = Persistence
            .createEntityManagerFactory("JPA_excer_3b");
    EntityManager em = emf.createEntityManager();
    try {
        **EmployeePK pk = new EmployeePK(employee.getId(),employee.getEmail());**
        em.getTransaction().begin();
        Employee anemployee = em.find(Employee.class, **pk**);
        em.remove(anemployee);
        em.getTransaction().commit();
    } catch (Exception e) {
        logging.error("This error is added a removing a employee :"
                + " :" + e);
    } finally {
        // Close all the connections:
        em.close();
        emf.close();
    }
}

我沒有得到任何錯誤，但我想知道這是否是正確的方法嗎？

Answer 1

是的，這是正確的方法。 EntityManager.find()方法需要實體的ID類的實例。 不是實體的一些隨機屬性。

請注意，錯誤不是由remove()方法引起的，而是由find()方法引起的。