“分离的实体传递给持久性错误”使用JPA / EJB代码 [英] "detached entity passed to persist error" with JPA/EJB code

问题描述

我正在尝试运行这个基本的JPA / EJB代码：

I am trying to run this basic JPA/EJB code:

public static void main(String[] args){
         UserBean user = new UserBean();
         user.setId(1);
         user.setUserName("name1");
         user.setPassword("passwd1");
         em.persist(user);
  }

我收到此错误：

javax.ejb.EJBException: javax.persistence.PersistenceException: org.hibernate.PersistentObjectException: detached entity passed to persist: com.JPA.Database

任何想法？

我在互联网上搜索，我找到的原因是：

I search on the internet and the reason I found was:

这是由您创建对象的方式引起的，即如果您明确设置了ID属性。删除ID分配修复了它。

This was caused by how you created the objects, i.e. If you set the ID property explicitly. Removing ID assignment fixed it.

但我没有得到它，我需要修改什么才能使代码正常工作？ / p>

But I didn't get it, what will I have to modify to get the code working?

推荐答案

假设你有两个实体专辑和照片。相册包含许多照片，因此它是一对多关系。

Let's say you have two entities Album and Photo. Album contains many photos, so it's a one to many relationship.

专辑类

@Entity
public class Album {
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    Integer albumId;

    String albumName;

    @OneToMany(targetEntity=Photo.class,mappedBy="album",cascade={CascadeType.ALL},orphanRemoval=true)
    Set<Photo> photos = new HashSet<Photo>();
}

照片类

@Entity
public class Photo{
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    Integer photo_id;

    String photoName;

    @ManyToOne(targetEntity=Album.class)
    @JoinColumn(name="album_id")
    Album album;

}

在保持或合并之前你要做的就是设置每张照片中的相册参考。

What you have to do before persist or merge is to set the Album reference in each photos.

        Album myAlbum = new Album();
        Photo photo1 = new Photo();
        Photo photo2 = new Photo();

        photo1.setAlbum(myAlbum);
        photo2.setAlbum(myAlbum);       

这是在您持久或合并之前附加相关实体的方法。

That is how to attach the related entity before you persist or merge.

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