从下拉列表数据库中删除重复项目

Question

我已经使用实体框架从数据库生成了下拉列表。我可以看到我的下拉列表，但我得到重复的值。我如何删除重复值？

controller: 

DBEntities db = new DBEntities(); 
var a = db.AspNetUsers.Select(h => new SelectListItem 
       { 
        Value = h.Nationality, 
        Text = h.Nationality 
       }).ToList(); 
      ViewData["nationselection"] = new SelectList(a, "Value", "Text"); 


View: 

@Html.DropDownList("selectedItem", (SelectList)ViewData["nationselection"], "-Selce-", new 
    { 

     onchange = @" 
      var form = document.forms[0]; 
      form.action='GetEmployeeDetails'; 
      form.submit();" 
    }) 

Answer 1

I understand you have duplicate values in your database. In EF u can select a distinct values from a db context. 

DBEntities db = new DBEntities(); 
var a = db.AspNetUsers.Select(h => new SelectListItem 
       { 
        Value = h.Nationality, 
        Text = h.Nationality 
       }).**Distinct().ToList();**