The moment you remove a child entity from the collection you will also be removing that child entity from the DB as well. orphanRemoval also implies that you cannot change parents; if there's a department that has employees, once you remove that employee to put it in another deparment, you will have inadvertantly removed that employee from the DB at flush/commit(whichver comes first). The morale is to set orphanRemoval to true so long as you are certain that children of that parent will not migrate to a different parent throughout their existence. Turning on orphanRemoval also automatically adds REMOVE to cascade list.

DDL ON DELETE CASCADE的等效JPA映射是CASCADE =CascadeType.REMOVE。孤儿删除意味着依赖实体在与其“父”实体的关系被破坏时被删除。例如，如果从@OneToMany关系中删除了一个子对象，而没有显式地在实体管理器中删除它。

orphanRemoval与ON DELETE CASCADE无关。

orphanremove是一个完全特定于orm的东西。当“父”实体不再引用“子”实体时，它标记“子”实体将被删除，例如，当你从父实体的相应集合中删除子实体时。

ON DELETE CASCADE是一个数据库特定的东西，它在删除父行时删除数据库中的“子”行。

@GaryK的答案绝对很棒，我花了一个小时来寻找一个解释orphanRemoval = true vs CascadeType。它帮助我理解。

总结:orphanRemoval = true与CascadeType工作相同。REMOVE ONLY当我们正在删除object (entityManager.delete(object))并且我们希望子对象也被删除时。

在完全不同的情况下，当我们获取一些数据，如List<Child> childs = object.getChilds()，然后使用orphanRemoval=true删除一个子(entityManager.remove(children .get(0))，将导致对应于children .get(0)的实体将从数据库中删除。

这里有一个例子:

当删除Employee实体对象时，删除操作将级联到引用的Address实体对象。在这方面，orphanRemoval=true和cascade=CascadeType。REMOVE是相同的，如果指定orphanremove =true，则CascadeType. REMOVE是相同的。REMOVE是多余的。

这两种设置之间的区别在于断开关系的响应。例如，将地址字段设置为null或另一个address对象。

如果orphanremove =true指定了断开连接的Address实例 自动删除。这对于清除依赖是有用的 对象(例如Address)，如果没有引用就不应该存在 所有者对象(例如Employee)。 如果只是cascade=CascadeType。指定了REMOVE，没有自动动作 因为断开一段关系并不意味着移除 操作。

为了避免由于孤立对象移除而导致的悬空引用，应该仅对包含私有非共享依赖对象的字段启用此特性。

我希望这能让你更清楚。

The moment you remove a child entity from the collection you will also be removing that child entity from the DB as well. orphanRemoval also implies that you cannot change parents; if there's a department that has employees, once you remove that employee to put it in another deparment, you will have inadvertantly removed that employee from the DB at flush/commit(whichver comes first). The morale is to set orphanRemoval to true so long as you are certain that children of that parent will not migrate to a different parent throughout their existence. Turning on orphanRemoval also automatically adds REMOVE to cascade list.