尝试一一删除元素:
List<String> Mylist = a.getMyList();em.getTransaction().begin();for (String element:Mylist){ em.remove(element);}em.getTransaction().commit();_____
解决方案(对我有用,感谢“ Genzotto”):
List<String> Mylist = a.getMyList();listStirng.clear();em.getTransaction().begin(); for (String str : Mylist) { em.merge(str); }em.getTransaction().commit();


