使用Spring Data-JPA更新单向@OneToMany对象列表时的常见行为是什么？

Question

我有一个带有另一个对象列表的对象.它映射如下:

@Entity
@Inheritance(strategy = InheritanceType.JOINED)
@Table(name = "products")
public class Product extends DateAudit {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @NotBlank
    @Size(min = 3, max = 30)
    private String name;

    @NotBlank
    private String shortDescription;

    @NotBlank
    private String description;

    @NotNull
    private Double regularPrice;

    private Double promotionPrice;

    @NotNull
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "category_id", nullable = false)
    private Category category;

    @NotNull
    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name = "store_id", nullable = false)
    private Store store;

    @Size(max = 20)
    private String sku;

    private Double weight;

    private Integer quantityInStock;

    @NotNull
    private Boolean notifyLowStock;

    @OneToMany(cascade = CascadeType.ALL)
    private List<Image> images = new ArrayList<Image>();

在图像方面,这是mapping:

@Entity
@Table(name = "images")
public class Image {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @NotBlank
    private String url;

会发生什么:1.我创建我的Product对象并将其保存在数据库中.2.我通过以后添加图像更新此产品对象,如下所示:

Product product = repository.findById(productId);
Image image = new Image();
image.setUrl(url);
product.getImages().add(image);
repository.save(product);

这是我每次在产品中添加新图像并保存时在控制台上获得的内容:

当我添加第一张图片时:

2018-07-27 22:46:47.367 DEBUG 8580 --- [nio-5000-exec-3] org.hibernate.SQL                        : insert into images (url) values (?)
2018-07-27 22:46:48.307 DEBUG 8580 --- [nio-5000-exec-3] org.hibernate.SQL                        : insert into products_images (product_id, images_id) values (?, ?)

当我再添加一张图片时:

2018-07-27 22:47:09.955 DEBUG 8580 --- [nio-5000-exec-4] org.hibernate.SQL                        : delete from products_images where product_id=?
2018-07-27 22:47:09.957 DEBUG 8580 --- [nio-5000-exec-4] org.hibernate.SQL                        : insert into products_images (product_id, images_id) values (?, ?)
2018-07-27 22:47:09.958 DEBUG 8580 --- [nio-5000-exec-4] org.hibernate.SQL                        : insert into products_images (product_id, images_id) values (?, ?)

当我添加第三张图片时:

2018-07-27 22:47:32.314 DEBUG 8580 --- [nio-5000-exec-5] org.hibernate.SQL                        : delete from products_images where product_id=?
2018-07-27 22:47:32.316 DEBUG 8580 --- [nio-5000-exec-5] org.hibernate.SQL                        : insert into products_images (product_id, images_id) values (?, ?)
2018-07-27 22:47:32.318 DEBUG 8580 --- [nio-5000-exec-5] org.hibernate.SQL                        : insert into products_images (product_id, images_id) values (?, ?)
2018-07-27 22:47:32.319 DEBUG 8580 --- [nio-5000-exec-5] org.hibernate.SQL                        : insert into products_images (product_id, images_id) values (?, ?)

我的问题是:是删除整个列表并将其全部添加回数据库的正确行为？我期待它只是添加新图像,将其他图像留在那里.相反,如果基于productId删除所有图像并将其全部添加回来.

我在更新之前检索产品.我检索产品,我将新图像添加到列表中,然后调用save方法.

这是正常的吗？有没有办法避免这种删除？

谢谢

Answer 1

简而言之,这需要列表中的订单,例如Image.url:

@OneToMany(cascade = CascadeType.ALL)
@OrderColumn(name = "url")
private List<Image> images = new ArrayList<>();

或者不要担心订单:

@OneToMany(cascade = CascadeType.ALL)
private Set<Image> images = new HashSet<>();

这些都消除了delete额外的insert反对products_images.

我对此有一个高级别解释的最接近的事情就在这里,虽然它是在讨论@Embeddable而不是@Entity集合中的元素.似乎Hibernate在集合中识别单个实体(带有id)的问题较少,但对于未排序List(或PersistentBag在Hibernate模型中)它不会这样做.