如何从 SQL Server 数据库绑定 ASP.NET MVC 中的下拉列表？

Question

I don't know how to make view from this code to show data in dropdown list. Please do tell me what changes I can make to solve my problem. I have tried some view but this causes errors.

Model:

public class Cities
{
    public int cityid { get; set; }
    public string Description { get; set; }
}

Controller:

public ActionResult Dropdownlist()
{
    List<Citites> cityname= new List<Citites>();
    string constring = ConfigurationManager.ConnectionStrings["dbx"].ConnectionString;

    SqlConnection con = new SqlConnection(constring);

    SqlCommand cmd = new SqlCommand("SELECT Cityid, Description FROM Cities", con);

    con.Open();

    SqlDataReader rdr = cmd.ExecuteReader();

    while (rdr.Read())
    {
        Citites ci = new Citites();
        ci.cityid = Convert.ToInt32(rdr["Cityid"]);
        ci.Description = rdr[1].ToString();                
        cityname.Add(ci);
    }

    return View(cityname);
}

View:

@model IEnumerable< RegisterForm_crud_mvc_.Models.Citites>
@{
    ViewBag.Title = "Dropdownlist";
}

<h2>Dropdownlist</h2>

@Html.DropDownListFor(model => model.cityid, Model.citynanme)

Answer 1

You have a bunch of issues in your code. Your view is strongly typed to a list of City objects and you are trying to use Model.citynanme . Your model is the list of city object and the list does not have a cityname property ( but each item in the list has)!

What you should ideally do is , Create a view model to represent the data needede in your view. In your case, you need a property to store the selected option value and another for data needed to build the options for the SELECT element. In your case it is the list of cities.

public class MyViewModel
{
  public List<SelectListItem> Cities { set;get;}
  public int SelectedCityId { set;get;}
}

Now in your GET action, you create an object of this, populate the Cities property by reading your table and send the view model object to the view.

public ActionResult Create()
{
  var vm = new MyViewModel();
  vm.Cities = GetCities();
  return View(vm);
}
private List<SelectListItem> GetCities()
{
    var options = new List<SelectListItem>();
    var constring = ConfigurationManager.ConnectionStrings["dbx"].ConnectionString;
    using (var c = new SqlConnection(constring))
    {
        using (var cmd = new SqlCommand("select Cityid, Description FROM Cities", c))
        {
            c.Open();
            var rdr = cmd.ExecuteReader();
            options = new List<SelectListItem>();
            while (rdr.Read())
            {
                var o = new SelectListItem
                {
                    Value = rdr.GetInt32(rdr.GetOrdinal("Cityid")).ToString(),
                    Text = rdr.GetString(rdr.GetOrdinal("Description"))
                };
                options.Add(o);
            }
        }
    }
    return options;
}

Now in your view, which is strongly typed to MyViewModel, you will use Html.DropDownListfor helper method where you will use the Cities property as the selectList parameter.

@model MyViewModel
@Html.DropDownListFor(model => model.SelectedCityId, Model.Cities)