java - hibernate :无法删除|删除分离的实例

Question

我正在制作一个简单的 api，可以在其中存储图像并对其执行增删改查功能。为了与数据库通信，我使用 Hibernate。虽然获取数据进展顺利，但我无法添加或删除数据。这将导致添加出现此异常；

org.hibernate.exception.GenericJDBCException: could not execute statement

以及删除的异常(exception)情况；

Removing a detached instance com.mycompany.server.model.Image#0

我不知道为什么它不能完成这项工作。它以前有效，我没有对其进行任何更改。希望你能找出问题所在。如果此信息还不够，请评论您想查看的内容。

这里有模型:

@Entity
@Table(name = "image")
@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
@NamedQueries({
@NamedQuery(name = "Image.findAll", query = "SELECT i FROM Image i")
, @NamedQuery(name = "Image.findByImageId", query = "SELECT i FROM Image i WHERE i.imageId = :imageId")
, @NamedQuery(name = "Image.findByContenttype", query = "SELECT i FROM Image i WHERE i.contenttype = :contenttype")
, @NamedQuery(name = "Image.findByName", query = "SELECT i FROM Image i WHERE i.name = :name")
, @NamedQuery(name = "Image.findByDescription", query = "SELECT i FROM Image i WHERE i.description = :description")})
public class Image implements Serializable {

    private static final long serialVersionUID = 1L;
    @Id
    @XmlElement(nillable=true)
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Basic(optional = false)
    @NotNull
    @Column(name = "image_id")
    private Integer imageId;

    @Basic(optional = false)
    @NotNull
    @Lob
    @Size(min = 1, max = 16777215)
    @Column(name = "content")
    private String content;

    @Basic(optional = false)
    @Size(min = 1, max = 45)
    @Column(name = "contenttype")
    private String contenttype;

    @Basic(optional = false)
    @NotNull
    @Size(min = 1, max = 45)
    @Column(name = "name")
    private String name;

    @Size(max = 45)
    @Column(name = "description")
    private String description;

    public Image() {
    }

    public Image(Integer imageId) {
        this.imageId = imageId;
    }

    public Image(Integer imageId, String content, String contenttype, String name) {
        this.imageId = imageId;
        this.content = content;
        this.contenttype = contenttype;
        this.name = name;
    }

    public Integer getImageId() {
        return imageId;
    }

    public void setImageId(Integer imageId) {
        this.imageId = imageId;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }

    public String getContenttype() {
        return contenttype;
    }

    public void setContenttype(String contenttype) {
        this.contenttype = contenttype;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

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

    @Override
    public boolean equals(Object object) {
        // TODO: Warning - this method won't work in the case the id fields are not set
        if (!(object instanceof Image)) {
            return false;
        }
        Image other = (Image) object;
        if ((this.imageId == null && other.imageId != null) || (this.imageId != null && !this.imageId.equals(other.imageId))) {
            return false;
        }
        return true;
    }

    @Override
    public String toString() {
        return "com.mycompany.server.model.Image[ imageId=" + imageId + " ]";
    }

}

以及服务实现:

public class ImageRepositoryServiceImpl implements ImageRepositoryService    {

    private EntityManagerFactory entityManagerFactory;

    private static ImageRepositoryServiceImpl instance;

    private ImageRepositoryServiceImpl() {
        entityManagerFactory = Persistence.createEntityManagerFactory("com.mycompany_server_war_1.0-SNAPSHOTPU");
    }

    static {
        instance = new ImageRepositoryServiceImpl();
    }

    private EntityManager getEntityManager() {
        return entityManagerFactory.createEntityManager();
    }

    public static ImageRepositoryService getInstance() {
        return instance;
    }

    @Override
    public List<Image> getAllImages() {
        EntityManager em = entityManagerFactory.createEntityManager();
       List<Image> images = em.createNamedQuery("Image.findAll", Image.class).getResultList();
        em.close();
        return images;
    }

    @Override
    public Image getImageFromId(int imageId) {
        EntityManager em = entityManagerFactory.createEntityManager();
        Image image = em.find(Image.class, imageId);
        em.close();        
        return image;
    }

    @Override
    public boolean addImage(Image image) {
        try{
            EntityManager em = entityManagerFactory.createEntityManager();
            em.getTransaction().begin();
            em.persist(image);
            em.getTransaction().commit();
            em.close();        
            return true;
        }catch(Exception e){
            return false;
    }              
}

    @Override
    public boolean editImage(Image image) {
        throw new UnsupportedOperationException("Not supported yet. edit"); //To change body of generated methods, choose Tools | Templates.
    }

    @Override
    public boolean DeleteImage(Image image) {
        try{
            EntityManager em = entityManagerFactory.createEntityManager();
            em.remove(image);
            return true;
        }catch(Exception e){
            return false;
        }
    }

}

编辑:

我解决了添加问题。显然 image_id 没有自动增加。现在我换成ai了，效果还不错。但删除仍然不起作用:'(

Answer 1

我在这段代码中看到了什么问题:

1. 您滥用实体管理器。每个实体应该属于一个实体管理者。如果您使用一个实体管理器加载实体，然后使用另一个实体管理器保存它，您可能会收到诸如正在删除分离的实例 com.mycompany.server.model.Image#0 之类的错误。
2. 只有在没有异常的情况下，才可以调用实体管理器的close。如果在调用 close 之前出现异常，您将导致资源泄漏。尝试使用 try-with-resources。
3. 您根据生成的标识符为实体实现了 equals 和 heshCode。这是不好的做法。如果您没有其他 Image 相等标准 - 请勿覆盖 equals 和 hashCode。

也许这篇笔记会对您有所帮助。