英文:

Hibernate detached entity i believe

问题

我在处理 Hibernate 方面时有点初学者，但我已经花了几个小时来解决一个问题，现在需要你的帮助。

我有一个管理文章的应用程序，每篇文章都是由某位作者编写的。
我想要做的是将一篇文章添加到数据库中，其中的 author_id 字段为空，然后仅在此之后再更新该字段。
然而，Hibernate 拒绝在数据库中更新我的实体。
```java
public <Article> void updateElement(Article entity) {
    EntityManager entityManager = createEntityManager();
    try {
        entityManager.getTransaction();
        entityManager.merge(entity);
        entityManager.getTransaction().commit();
    }
    catch(RuntimeException e ){
        entityManager.getTransaction().rollback();
    }
    finally {
        entityManager.close();
    }
}

这是我尝试更新条目的方式。我会收到一篇文章作为参数，我确定它肯定在数据库中。然后我尝试执行合并操作以进行更新。但我不知道这是否是正确的方法。请帮助我。

文章类：

@ToString
@AllArgsConstructor
@NoArgsConstructor
@Setter
@Getter
@Entity
@Table(name = "Article")
public class Article {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "article_id")
    private Integer id;

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

    @NotBlank
    @Column(name = "publication_date")
    private Date publicationDate;

    @ManyToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    @JoinColumn(name = "author_id")
    private Author author;

    @ManyToMany(fetch = FetchType.EAGER)
    @Enumerated(EnumType.STRING)
    @JoinTable(name = "article_tags",
                joinColumns = @JoinColumn(name = "article_id"),
                inverseJoinColumns = @JoinColumn(name = "tag_id"))
    private Set<Tag> tags = new HashSet<>();
}

以及作者类：

@AllArgsConstructor
@NoArgsConstructor
@Setter
@Getter
@Entity
@Table(name = "Authors")
public class Author {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE,
            generator = "entity_id_seq")
    @Column(name = "author_id", updatable = false)
    private int id;

    @NotBlank
    @Column(name = "author_name")
    private String name;

    @OneToMany(mappedBy = "author", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    private Set<Article> writtenArticles = new HashSet<>();
}

<details>
<summary>英文:</summary>

I am kinda beginner when it comes to hibernate, but i have been dealing with a problem for several hours, and i need your help.

I have an application that manages articles, and each article is written by an author. 
What i want to do is to add an article to a database, with its author_id field being null, and only after that to update that field.
However, hibernate refuses to update my entity in the database.

public <Article> void updateElement(Article entity) {
EntityManager entityManager = createEntityManager();
try {
entityManager.getTransaction();
entityManager.merge(entity);
entityManager.getTransaction().commit();
}
catch(RuntimeException e ){
entityManager.getTransaction().rollback();
}
finally {
entityManager.close();
}
}

This is how i try to update the entry. I receive an Article as a parameter, for which i know for sure that it is in the database. And after that i try to do merge in order to update it. But i don't know if it the right approach. Please help me.

The article class:

@ToString
@AllArgsConstructor
@NoArgsConstructor
@Setter
@Getter
@Entity
@Table( name = "Article")
public class Article {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "article_id")
private Integer id;

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

@NotBlank
@Column(name = "publication_date")
private Date publicationDate;

@ManyToOne(cascade = CascadeType.ALL,fetch = FetchType.LAZY)
@JoinColumn(name = "author_id")
private Author author;

@ManyToMany(fetch = FetchType.EAGER)
@Enumerated(EnumType.STRING)
@JoinTable(name = "article_tags",
            joinColumns = @JoinColumn(name = "article_id"),
            inverseJoinColumns = @JoinColumn(name ="tag_id"))
private Set<Tag> tags = new HashSet<>();

}

and the author class
```@AllArgsConstructor
@NoArgsConstructor
@Setter
@Getter
@Entity
@Table(name = "Authors")
public class Author {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE,
            generator = "entity_id_seq")
    @Column(name = "author_id",updatable = false)
    private int id;

    @NotBlank
    @Column(name = "author_name")
    private String name;

    @OneToMany(mappedBy = "author",cascade = CascadeType.ALL,fetch = FetchType.LAZY)
    private Set<Article> writtenArticles = new HashSet<>();

}```

</details>


# 答案1
**得分**: 1

请开始您的事务，不仅获取事务：
将

            entityManager.getTransaction();
替换为

            entityManager.getTransaction().begin();

<details>
<summary>英文:</summary>

please begin your transaction and not only get the transaction:
replace the

            entityManager.getTransaction();
by

            entityManager.getTransaction().begin();


</details>