1

当我在 JPA 中将 Idclass 用于具有复合键的实体时，我编写了一个删除方法，例如：

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();
    }
}

我得到错误：

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

当我将代码更改为：

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();
    }
}

我没有收到任何错误，但我想知道这是否是正确的方法？

4

1 回答 1

3

是的，这是正确的做法。该EntityManager.find()方法需要实体 ID 类的实例。不是实体的一些随机属性。

请注意，错误不是由remove()方法引起的，而是由find()方法引起的。

于 2012-12-16T14:25:00.140 回答