保存实体后，Hibernate 为使用 @Formula 注释的实体属性返回 null

Question

我有一个简单的类，如下所示：

@Entity
@Table(name = "post")
public class Post {

    @Id
    @GeneratedValue
    Long id;

    @Column(name = "title")
    String title;

    @Formula("(select current_date())")
    Date currentDate;

    @OneToMany(mappedBy = "post")
    Set<PostComment> commentList = new HashSet<>();
}

并希望在服务中更新此实体：

@Service
@Transactional
public class PostService {

    private final PostRepository postRepository;

    public PostService(PostRepository postRepository) {
        this.postRepository = postRepository;
    }

    @Transactional
    public Post save(Post entity) {
        Post post = postRepository.saveAndFlush(entity);
        System.out.println("current_date: " + post.getCurrentDate());
        post.getCommentList().forEach(pc -> System.out.println(pc.getReview()));
        return post;
    }
}

当我检查休眠日志时，它首先selectPost 实体的所有字段，但是当我调用post.getCurrentDate()（它用@Formula 注释）返回null：

Hibernate: select post0_.id as id1_0_0_, post0_.title as title2_0_0_, (select current_date()) as formula0_0_ from post post0_ where post0_.id=?
Hibernate: update post set title=? where id=?
current_date: null
Hibernate: select commentlis0_.post_id as post_id3_1_0_, commentlis0_.id as id1_1_0_, commentlis0_.id as id1_1_1_, commentlis0_.post_id as post_id3_1_1_, commentlis0_.review as review2_1_1_ from post_comments commentlis0_ where commentlis0_.post_id=?
review

为什么它返回并记录commentList 但不返回currentDate？是休眠错误吗？

注意

我将完整的示例项目推送到了github中你可以看到here。

Answer 1

我写了a test case on my high-performance-java-persistence GitHub repository，它就像一个魅力。

实体如下所示：

@Entity(name = "Event")
@Table(name = "event")
public static class Event {

    @Id
    private Long id;

    @Formula("(SELECT current_date)")
    @Temporal(TemporalType.TIMESTAMP)
    private Date createdOn;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public Date getCreatedOn() {
        return createdOn;
    }

    public void setCreatedOn(Date createdOn) {
        this.createdOn = createdOn;
    }
}

注意Date 属性也使用@Temporal 注释。

现在为了模拟您的用例，我编写了以下数据访问逻辑：

Event event = new Event();
event.setId(1L);

entityManager.persist(event);
entityManager.flush();

entityManager.refresh(event);

assertNotNull(event.getCreatedOn());

注意refresh 调用，因为实体缓存在persist 上，因此我们希望从数据库中重新获取它。

并且，在执行时，Hibernate 会生成以下语句：

Query:["insert into event (id) values (?)"], Params:[(1)]
Query:["select formulacur0_.id as id1_0_0_, (SELECT current_date) as formula0_0_ from event formulacur0_ where formulacur0_.id=?"], Params:[(1)]

并且测试用例运行得很好。只需在您的用例和我的用例之间进行比较调试，看看为什么您的用例不起作用而我的用例起作用。