一开始我自定义BeforeSaveCallback，在里面修改了object的内容，但发现并没有保存在数据库中。在官方的文档中说，在这事件里面修改object内容只是临时的不会做持久化，需要修改转换后document的内容才会保存进数据库，官方原话：Entity callback method invoked before a domain object is saved. Can return either the same or a modified instance of the domain object and can modify Document contents. This method is called after converting the entity to a Document so effectively the document is used as outcome of invoking this callback. Changes to the domain object are not taken into account for saving, only changes to the document. Only transient fields of the entity should be changed in this callback. To change persistent the entity before being converted, use the BeforeConvertCallback.
官方文档
为了避免实体转document后字段名发生改变不好找，就选用了BeforeConvertEvent，在转换前进行了处理，但其实在BeforeSaveEvent处理也是可以的
事件的发生顺序
Event: BeforeDeleteEvent AfterDeleteEvent BeforeConvertEvent BeforeSaveEvent AfterSaveEvent AfterLoadEvent