错误提示：The database operation was expected to affect 1 row(s), but actually affected 0 row(s); data may have been modified or deleted since entities were loaded. See http://go.microsoft.com/fwlink/?LinkId=527962 for information on understanding and handling optimistic concurrency exceptions.

需求很简单，我有一个主表Module 模块表，有一个子表Menu菜单，我想要通过Module实体级联更新Menu表，Menu对象由前端直接传值给我

代码如下：

 [HttpPut]
        public void HttpPut()
            Module module = _context.modules.Include(x => x.List).FirstOrDefault(x => x.Guid == Guid.Parse("1e8c7053-8323-4438-af75-94afabeb9d7e"));
            module.List.Clear();
            var menu = new Menu { Name = "345", Guid = Guid.NewGuid() };
            module.List.Add(menu);
            _context.SaveChanges();
 [Table("Menu")]
    public class Menu
        [Key]
        public Guid Guid { get; set; }
        public Module Module { get; set; }
        public string Name { get; set; }
  [Table("Module")]

    public class Module
        public Module()
            List = new List<Menu>();
        [Key]
        public Guid Guid { get; set; }
        public string Name { get; set; }
        [ConcurrencyCheck]
        public List<Menu> List { get; set; }
　　看似平平无常的代码，却一直提示了出错，搜索了一些相关的文章，也没有找的对应的解决方案，最后在官方文档中找到了对应的例子
官方示例代码如下：
using (var context = new BloggingContext())
    var blog = context.Blogs.Include(b => b.Posts).First();
    var post = new Post { Title = "Intro to EF Core" };
    blog.Posts.Add(post);
    context.SaveChanges();
　　感觉和自己写的也是差不多，最后仔细发现原来自己在新增Menu的时候给主键赋值了，所以EF会判定你这条数据是去更新的，所以提示匹配到了0行数据，最后把主键的赋值去掉就可以保存成功了