Java 使用 JPA 从集合中删除子项
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Removing child from collection using JPA
提问by Andrey
I'm using JPA over Hibernate in my web-app. Here are two entities (only getters are shown):
我在我的网络应用程序中通过 Hibernate 使用 JPA。这里有两个实体（只显示了 getter）：
class Child {
private Parent parent;
@ManyToOne(optional=false)
@JoinColumn(name="parent_id", referencedColumnName="parent_id", nullable=false, updatable=false)
public Parent getParent() {
return parent;
}
}
class Parent {
private Collection<Child> children;
@OneToMany(fetch=FetchType.EAGER, mappedBy="parent", cascade={CascadeType.ALL})
public Collection<Child> getChildren() {
return children;
}
}
As you see Parentand Childrelate as "one-to-many".
如您所见，Parent并将其Child关联为“一对多”。
Now I need to load a Parentinstance, remove some or all children and save the changes. Below is code which does not work for me:
现在我需要加载一个Parent实例，删除部分或全部子项并保存更改。以下是对我不起作用的代码：
Parent p = entityManager.find(Parent.class, 12345L); // load entity
p.getChildren().clear(); // remove all children
entityManager.merge(p); // try to save
Child entities are not remove in the example above. Now I have to manually call entityManager.remove()for each child.
在上面的示例中没有删除子实体。现在我必须手动entityManager.remove()为每个孩子打电话。
Is there any easier way to manage child collection?
有没有更简单的方法来管理子集合？
Please notice that I don't want to use Hibernate-specific functionality, only pure JPA.
请注意，我不想使用 Hibernate 特定的功能，只想使用纯 JPA。
采纳答案by Bozho
For JPA 2.0 you can set orphanRemoval=trueof the @OneToMany
对于JPA 2.0你可以设置 orphanRemoval=true的@OneToMany
For JPA 1.0, you should use hibernate-specific annotations. That is the @Cascadeannotation (instead of the cascadeattribute), with a value of
对于 JPA 1.0，您应该使用特定于休眠的注释。那是@Cascade注释（而不是cascade属性），其值为
@Cascade({CascadeType.ALL, CascadeType.DELETE_ORPHAN})
Hibernate 3.5+ implement JPA 2.0
Hibernate 3.5+ 实现 JPA 2.0
