Question

我有一个类User，它充当数据库中Users表的Persistence模型：

public class User {
@Id
@Basic(optional = false)
@Column(name = "USER_ID")
private Long userId;

@JoinColumn(name = "LAST_CHANGED_USER_ID", referencedColumnName = "USER_ID")
@ManyToOne(fetch = FetchType.LAZY)
private User lastChangedUser;
...

@Override
public int hashCode() {
    int hash = 0;
    hash += (userId != null ? userId.hashCode() : 0);
    return hash;
}

@Override
public boolean equals(Object object) {
    if (!(object instanceof User)) {
        return false;
    }

    User other = (User) object;
    if ((this.userId == null && other.userId != null) || 
        (this.userId != null && !this.userId.equals(other.userId))) {
        return false;
    }
    return true;
}

@Override
public String toString() {
    return "User[userId=" + userId + "]";
}
}

只要对User实例进行了更改，就会更新字段lastChangedUser。请考虑以下方法：

private void setUsername(string username, User lastChangedUser){
    this.username = username;
    this.lastChangedUser = lastChangedUser;
}

public void updateUserName(Long userId, Long lastChangedUserId, String username){
    EntityManager em = PersistenceManager.getPersistenceManager()
       .getEntityManager();
    EntityTransaction transaction = em.getTransaction();

    User user = em.find(User.class, userId);
    User lastChangedUser = em.find(User.class, lastChangedUserId);

    transaction.begin();
    user.setUsername(username, lastChangedUser);
    transaction.commit();
}

和单元测试：

public void testUpdateUsername(){
    UserFacade instance = new UserFacade();
    User john = instance.getUserByUserId(new Long(1));
    User jane = instance.getUserByUserId(new Long(2));

    // make the update and persist
    instance.updateUsername("JANE M. DOE", jane.userId, john.userId);

    // assert that john made the change to jane
    jane = instance.getUserByUserId(new Long(2));

    assertTrue(jane.username.equals("JANE M. DOE"));

    User actual = jane.lastChangedUser;
    User expected = john;

    // this assertion passes...
    assertTrue(actual.equals(expected));

    // yet this assertion fails!
    assertTrue(expected.equals(actual));

    // this fails as well.
    assertEquals(expected, actual);
}

使用Netbeans 7.1.1，测试结果屏幕返回错误消息：

FAILED: expected: User[id=1], but was: User[id=1].

检查时，对象actual的类型不是User，而是代理对象的类型。我假设这是由于LAZY获取注释。因此，对象的userid的值为null，expected.equals(actual)返回false。但是，actual.equals(expected)会返回true。为了增加我的困惑，失败消息显示actual.userId不是null，而是等于预期的ID！

Hibernate或JUnit的一些怪癖导致实际的User对象在失败后出现？

Answer 1

有些朋友和我通过a question about obtaining ids without fetching the entire object找到了解决方案。由于对象是代理，因此直接在userid中重新生成字段equals会产生空值。但是，对用户标识使用 getter方法会导致从数据库中获取实际值。因此，equals方法应如下所示：

@Override public boolean equals(Object object){ if (!(object instanceof User)) { return false; } User other = (User) object; if ((this.getUserId() == null && other.getUserId() != null) || (this.getUserId() != null && !this.getUserId().equals(other.getUserId()))) { return false; } return true; }

现在断言将成立。

JPA：与Proxy对象的等式断言

1 个答案: