Question

我有非常简单的模型，我想修改（删除）一个元素集合，这是其中之一的财产。

public class Student
{
   [Key]
   [Column(Order = 1)]
   public int Id { get; set; }
   public string FirstName { get; set; }
   public string SecondName { get; set; }
   public int DepartamentID { get; set; }
}

public class Departament
{
   [Key]
   [Column(Order = 1)]
   public int Id { get; set; }
   public string Title { get; set; }
   public virtual ICollection<Student> Students { get; set; }
}

private void Remove(List<int> IDsOfStudentsToRemove)
{
    foreach (int id in IDsOfStudentsToRemove)
    {
       var Student = StudentContext.Students.Find(id);

       var Departament = DepartamentsContext
            .Departaments.Find(Student.DepartamentID);

       // That's what I'd want to achieve:
       // Remove student from Departament's Students collection
       // then remove student from Students Table

       Departament.Students.Remove(Student);
       StudentContext.Students.Remove(Student);
    }

    StudentContext.SaveChanges();
    DepartamentContext.SaveChanges();
}

但那是我收到的错误

System.InvalidOperationException：＆＃39;操作失败：由于一个或多个关系无法改变外键属性是不可为空的。当对a进行更改时关系，相关的外键属性设置为空值。如果外键不支持空值，则为新关系必须定义外键属性必须另外分配必须删除非空值或不相关的对象。＆＃39;

非常相似的主题：

The relationship could not be changed because one or more of the foreign-key properties is non-nullable

提前致谢

删除作为模型字段的集合元素

0 个答案: