JPA與IdClass問題刪除查詢

Question

當我在JPA使用Idclass與複合鍵的實體，我寫這樣一個remove方法：

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(); 
    } 
} 

我得到的錯誤：

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 

當我將代碼更改爲：

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，但我不知道這是否是正確的方法來做到這一點？

Answer 1

是的，這是正確的做法。 EntityManager.find()方法需要實體的ID類的實例。不是該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()方法造成的。