JPA中的CascadeType.REMOVE和orphanRemoval有什么区别? [英] What is the difference between CascadeType.REMOVE and orphanRemoval in JPA?

问题描述

两者之间有什么区别

@OneToMany(cascade=REMOVE, mappedBy="customer")
public List<Order> getOrders() { ... }

和

@OneToMany(mappedBy="customer", orphanRemoval="true")
public List<Order> getOrders() { ... }

此示例来自Java EE教程，但我仍然不了解详细信息.

This example is from Java EE Tutorial, but I still don't understand details.

推荐答案

来自此处:-

级联删除

使用CascadeType.REMOVE(或CascadeType.ALL， (其中包括REMOVE)表示删除操作应为 自动级联到该对象所引用的实体对象 字段(集合可以引用多个实体对象 字段):

Marking a reference field with CascadeType.REMOVE (or CascadeType.ALL, which includes REMOVE) indicates that remove operations should be cascaded automatically to entity objects that are referenced by that field (multiple entity objects can be referenced by a collection field):

@Entity
class Employee {
     :
    @OneToOne(cascade=CascadeType.REMOVE)
    private Address address;
     :
}

移除孤儿

JPA 2支持其他更积极的删除级联模式 可以使用 @OneToOne和@OneToMany批注:

JPA 2 supports an additional and more aggressive remove cascading mode which can be specified using the orphanRemoval element of the @OneToOne and @OneToMany annotations:

@Entity
class Employee {
     :
    @OneToOne(orphanRemoval=true)
    private Address address;
     :
}

差异:-

这两个设置之间的区别在于对 断开关系.例如，当设置 地址字段设置为null或另一个Address对象.

The difference between the two settings is in the response to disconnecting a relationship. For example, such as when setting the address field to null or to another Address object.

• 如果指定了 orphanRemoval = true ，则会自动删除断开连接的Address实例.这对于清理很有用 没有一个不应该存在的相关对象(例如地址) 来自所有者对象(例如员工)的引用.
• 如果仅指定 cascade = CascadeType.REMOVE ，则不会执行任何自动操作，因为断开关系不是删除操作
  操作.

• If orphanRemoval=true is specified the disconnected Address instance is automatically removed. This is useful for cleaning up dependent objects (e.g. Address) that should not exist without a reference from an owner object (e.g. Employee).
• If only cascade=CascadeType.REMOVE is specified no automatic action is taken since disconnecting a relationship is not a remove
  operation.

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