1 public abstract class Base { }
 2     public class User : Base
 3     {
 4         public Role Role { get; set; }
 5     }
 6     public class Role : Base
 7     {
 8         public List<User> Users { get; set; }
 9         public List<Right> Rights { get; set; }
10     }
11     public class Right : Base
12     {
13         public List<Role> Roles { get; set; }
14     }
15     public class DAL<T> where T : Base
16     {
17         public int Add(T obj)
18         {
19             Context.DbSet<T>().Add(obj);
20             Context.SaveChanges();//报错
21             //一个实体对象不能由多个 IEntityChangeTracker 实例引用。
22         }
23     }