JPA OneToMany不删除子项 [英] JPA OneToMany not deleting child

问题描述

我在父实体和子实体之间的简单 @OneToMany 映射时遇到问题。一切正常，只有当我从集合中删除它们时才删除子记录。

I have a problem with a simple @OneToMany mapping between a parent and a child entity. All works well, only that child records are not deleted when I remove them from the collection.

父母：

@Entity
public class Parent {
    @Id
    @Column(name = "ID")
    private Long id;

    @OneToMany(cascade = {CascadeType.ALL}, mappedBy = "parent")
    private Set<Child> childs = new HashSet<Child>();

 ...
}

孩子：

@Entity
public class Child {
    @Id
    @Column(name = "ID")
    private Long id;

    @ManyToOne(cascade = CascadeType.ALL)
    @JoinColumn(name="PARENTID", nullable = false)
    private Parent parent;

  ...
}

如果我现在删除并且来自子集的子集，它不会从数据库中删除。我试图取消 child.parent 引用，但这也无效。

If I now delete and child from the childs Set, it does not get deleted from the database. I tried nullifying the child.parent reference, but that did not work either.

实体用于Web应用程序，删除是作为Ajax请求的一部分发生的。按下保存按钮时，我没有已删除子项的列表，因此我无法隐式删除它们。

The entities are used in a web application, the delete happens as part of an Ajax request. I don't have a list of deleted childs when the save button is pressed, so I can't delete them implicitly.

推荐答案

JPA的行为是正确的（意味着根据规范）：对象不会被简单删除因为您已从OneToMany集合中删除它们。有特定于供应商的扩展可以做到这一点，但原生JPA不适合它。

JPA's behaviour is correct (meaning as per the specification): objects aren't deleted simply because you've removed them from a OneToMany collection. There are vendor-specific extensions that do that but native JPA doesn't cater for it.

部分原因是因为JPA实际上并不知道它是否应删除某些内容从集合中删除。在对象建模术语中，这是组合和聚合*。

In part this is because JPA doesn't actually know if it should delete something removed from the collection. In object modeling terms, this is the difference between composition and "aggregation*.

在组合中的区别，孩子没有父母就没有实体。一个典型的例子是House和Room之间。删除House和Rooms也是。

In composition, the child entity has no existence without the parent. A classic example is between House and Room. Delete the House and the Rooms go too.

聚合是一种较为宽松的关联，以课程和学生为代表。删除课程，学生仍然存在（可能在其他课程中）。

Aggregation is a looser kind of association and is typified by Course and Student. Delete the Course and the Student still exists (probably in other Courses).

所以你需要使用供应商 - 强制执行此行为的特定扩展（如果可用）或显式删除子项并将其从父项集合中删除。

So you need to either use vendor-specific extensions to force this behaviour (if available) or explicitly delete the child AND remove it from the parent's collection.

我知道：

• Hibernate ：cascade delete_orphan。参见 10.11。传递性持久性;和


• EclipseLink ：称之为私人所有权。请参阅如何使用@PrivateOwned注释。

• Hibernate: cascade delete_orphan. See 10.11. Transitive persistence; and
• EclipseLink: calls this "private ownership". See How to Use the @PrivateOwned Annotation.

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