如何在asp.net core MVC中从另一个具有验证的模型创建下拉列表？

模型类.cs

public class Class
    {
        public int ClassId { get; set; }

        [NotMapped]
        public string EncryptedId { get; set; }

        [Required]
        [Display(Name = "Class Name")]
        public string ClassName { get; set; }
    }

public class Subject
    {
        public int SubjectId { get; set; }

        [NotMapped]
        public string EncryptedId { get; set; }
        public string SubjectName { get; set; }
        public int ClassId { get; set; }
        public Class Class { get; set; }
    }

public class CreateSubjectViewModel
    {
        public int SubjectId { get; set; }

        [NotMapped]
        public string EncryptedId { get; set; }

        [Required]
        [Display(Name = "Subject Name")]
        public string SubjectName { get; set; }

        public int ClassId { get; set; }

        public int ClassesId { get; set; }
        public virtual List<Class> Classes { get; set; }
    }

模型主题.cs

public class Class
    {
        public int ClassId { get; set; }

        [NotMapped]
        public string EncryptedId { get; set; }

        [Required]
        [Display(Name = "Class Name")]
        public string ClassName { get; set; }
    }

public class Subject
    {
        public int SubjectId { get; set; }

        [NotMapped]
        public string EncryptedId { get; set; }
        public string SubjectName { get; set; }
        public int ClassId { get; set; }
        public Class Class { get; set; }
    }

public class CreateSubjectViewModel
    {
        public int SubjectId { get; set; }

        [NotMapped]
        public string EncryptedId { get; set; }

        [Required]
        [Display(Name = "Subject Name")]
        public string SubjectName { get; set; }

        public int ClassId { get; set; }

        public int ClassesId { get; set; }
        public virtual List<Class> Classes { get; set; }
    }

ViewModel CreateSubjectViewModel.cs

public class Class
    {
        public int ClassId { get; set; }

        [NotMapped]
        public string EncryptedId { get; set; }

        [Required]
        [Display(Name = "Class Name")]
        public string ClassName { get; set; }
    }

public class Subject
    {
        public int SubjectId { get; set; }

        [NotMapped]
        public string EncryptedId { get; set; }
        public string SubjectName { get; set; }
        public int ClassId { get; set; }
        public Class Class { get; set; }
    }

public class CreateSubjectViewModel
    {
        public int SubjectId { get; set; }

        [NotMapped]
        public string EncryptedId { get; set; }

        [Required]
        [Display(Name = "Subject Name")]
        public string SubjectName { get; set; }

        public int ClassId { get; set; }

        public int ClassesId { get; set; }
        public virtual List<Class> Classes { get; set; }
    }

公共类CreateSubjectViewModel
{
public int SubjectId{get；set；}
[未映射]
公共字符串EncryptedId{get；set；}
[必需]
[显示（Name=“主题名称”）]
公共字符串SubjectName{get；set；}
public int ClassId{get；set；}
public int ClassesId{get；set；}
公共虚拟列表类{get；set；}
}

控制器代码

[HttpGet]
public IActionResult CreateSubject()
{

    List<Class> classList = _context.Classes.ToList();
    ViewData["classList"] = classList.Select(x => new SelectListItem { Value = x.EncryptedId, Text = x.ClassName });
    return View();
}

[HttpPost]
public IActionResult CreateSubject(CreateSubjectViewModel model)
{
    if (ModelState.IsValid)
    {
        Subject newSubject = new Subject
        {
            //SubjectName = model.SubjectName,
            //here code for store data in subject table
        };
        _cdsRepository.AddSubject(newSubject);
        return RedirectToAction("ListClasses", "UDP");
    }

    return View(model);
}

[HttpGet]
public IActionResult CreateSubject（）
{
List classList=_context.Classes.ToList（）；
ViewData[“classList”]=classList.Select（x=>newselectListItem{Value=x.encryptedd，Text=x.ClassName}）；
返回视图（）；
}
[HttpPost]
公共IActionResult CreateSubject（CreateSubjectViewModel模型）
{
if（ModelState.IsValid）
{
主题newSubject=新主题
{
//SubjectName=model.SubjectName，
//这里是在主题表中存储数据的代码
};
_cdsRepository.AddSubject（newSubject）；
返回重定向操作（“列表类”、“UDP”）；
}
返回视图（模型）；
}

如何从

Class.cs

获取数据，并在单击按钮时正确验证下拉列表并在下拉列表中显示数据

如果一切正常，则使用类Id值将数据存储在

Subject.cs

中