在 MVC 中选择项目时从数据库中获取图像 ASP.NET

问：

我是 MVC 的新手 ASP.NET 对它了解不多。我想从数据库中获取 3 张图像，从列表中选择项目并显示在网页上。我将列表框项的 Id 和表的主键设置相同。这是我尝试过的代码，但它不起作用，我应该进行什么修改。（图像的URl存储在数据库中）

模型等级：

public class UserDetailModel
{
    public string LetterId { get; set; }
    public string LetterPic { get; set; }
    public string LetterRecord { get; set; }
    public string LetterWord { get; set; }
    public string LetterWord_Pic { get; set; }
    public string LetterWordRecord { get; set; }

    [Display(Name = "LetterDetail")]
    public List<LetterList> letterDetail;
    [Display(Name = "selectedLetter")]
    public string selectedLetter { get; set; }
}

public class LetterList
{
    public string listId { get; set; }
    public string listName { get; set; }
} 

控制器：

 public ActionResult letter(string SelectedLetter)
 {   
     demo.Models.UserDetailModel obj = new demo.Models.UserDetailModel();
     obj.letterDetail = new List<LetterList>()
         {
             new LetterList() { listId = "1", listName =  "A" },
             new LetterList() { listId = "2",  listName= "B" },
             new LetterList() { listId = "3",  listName= "C" },
             new LetterList() { listId ="4",  listName= "D"}
         };
    return View(obj);

    using (var context = new VirtualSpeechTherapistEntities())
    {
         var hurf = from b in context.hurf_e_tahaji
                    where b.Letter_Id = SelectedLetter 
                    select b;
         return View("letter", context);
   };   

主键应该等于选定的listItem id，where子句写什么？//

视图：

@model demo.Models.UserDetailModel

@Html.ListBoxFor(obj => obj.selectedLetter, new SelectList (Model.letterDetail, "listId","listName")) ;

@Html.Id(Model.selectedLetter);

<img src="@Url.Content(Model.LetterPic)"/>