spring-data-jpa，克隆ManyToMany映射表

Question

下面是JPA实体(使用spring JPA1.9.1.RELEASE和Hibernate 4.3.11.Final)

@Getter @Setter @Entity @Table(name = "product")
class Product {

  @Id @GeneratedValue
  private Long id;

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

  @ManyToMany(cascade = CascadeType.PERSIST)
  @JoinTable(
    name = "product_attachment",
    joinColumns = {
      @JoinColumn(name = "product_id", referencedColumnName = "id")
    },
    inverseJoinColumns = {
      @JoinColumn(name = "attachment_id", referencedColumnName = "id")
    }
  )
  private List<Attachment> attachments;
}

我需要克隆product和product_attachment列。(不是attachment，所以它是主表)

private Product _clone(Product src) {

  Product dst = new Product();
  BeanUtils.copyProperties(src, dst, "id", "attachments");

  dst.setAttachments(src.getAttachments());

  return productRepository.save(dst);
}

但我不例外。

org.hibernate.HibernateException: Found shared references to a collection: Product.attachments

我解决这个问题的方法是再次获得相同的实体。密码在下面。

private Product _clone(Product src) {

  Product dst = new Product();
  BeanUtils.copyProperties(src, dst, "id", "attachments");

  dst.setAttachments(
    attachmentRepository.findAll(
      src.getAttachments().stream()
        .map(Attachment::getId).collect(Collectors.toList())
    )
  );

  return productRepository.save(dst);
}

但这似乎是多余的，谁知道更好的方法？

Answer 1

您不能克隆集合attachments itselfe，而必须复制其内容。(我认为原因是Hibernate使用一些黑客来检测集合内容上的更改)。

 dst.attachments = new ArrayList(src.attachments);

Answer 2

问题是，复制的列表引用了源产品(浅)中的附件。

您应该使用与手动复制Product相同的方法复制附件条目：

Product dst = new Product();
BeanUtils.copyProperties(src, dst, "id", "attachments");
dst.setAttachments(new ArrayList<Attachment>(src.getAttachments().size()));
for(Attachment a : src.getAttachments()){
    Attachment dstA = new Attachment();
    BeanUtils.copyProperties(a, dstA, {Your properties});
    a.getAttachments().add(dstA);
}

或者您可以使用帮助类，如Apache方法来执行源产品的深度复制。