Get a default NULL value from DropDownList in ASP.NET MVC

Question

I am creating a Trailer for existing Driver (that can be selected from Drop Down list).

@Html.DropDownListFor(x => x.Driver.driverID, (SelectList)ViewBag.DriverID, "-- Please Select -- ", new { @class = "form-control" })

For CREATE function it works perfectly.

//Create Get
public ActionResult Create()
{
    ViewBag.DriverID = new SelectList(db.Drivers, "driverID", "driverFullName");
    return View();
}

For EDIT function (edit trailers number and leave the driver NULL) it does not work.

//Edit Get
public ActionResult Edit(int? id)
{
     if (id == null)
     {
         return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
     }
     Trailer trailer = db.Trailers.Find(id);
     if (trailer == null)
     {
         return HttpNotFound();
     }
     ViewBag.DriverID = new SelectList(db.Drivers.ToList(), "driverID", "driverFullName");
     return View(trailer);
}

I have the -- Please Select -- on the drop down list as a first empty value.
How could I put a NULL value on this first empty value (so the trailer would have NO driver selected) from drop down list?

Please show us Create and Edit actions in your controller and how you populate ViewBag.DriverID. — jomsk1e
– jomsk1e, Commented Mar 6, 2017 at 17:49
If --Please Select-- was selected that means its NULL right? Why you want null? — jomsk1e
– jomsk1e, Commented Mar 6, 2017 at 18:04
--Please Select-- is just an empty slot. I want a NULL for the trailer none driver be selected. — Effy Sille
– Effy Sille, Commented Mar 6, 2017 at 18:27
can you provide Drivers model and you want to select --Please Select-- will will return null ? but you cant submit when its --Please Select-- right? — Usman
– Usman, Commented Mar 6, 2017 at 18:28

Usman · Accepted Answer · 2017-03-06 19:04:10Z

4

this is because your driverID property in Drivers class is not nullable ? that is why when you select -- Please Select -- it gives validation message The driverID field is required so you should set driverID to nullable like

public int? driverID {get;set;}

now its default value will be null when you select -- Please Select --

Edit

another way is to add a default object manually like

in view

 @Html.DropDownListFor(x => x.Driver.driverID, (SelectList)ViewBag.DriverID, new { @class = "form-control" })

and in edit action

public ActionResult Edit(int? id)
{
     if (id == null)
     {
         return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
     }
     Trailer trailer = db.Trailers.Find(id);
     if (trailer == null)
     {
         return HttpNotFound();
     }

     var list = db.Drivers.ToList();
     list.Insert(0, new Drivers() {driverFullName = "-- Please Select --"});
     ViewBag.DriverID = new SelectList(list, "driverID", "driverFullName"); //showing the list of drivers on edit page
     return View(trailer);
}

edited Mar 6, 2017 at 19:04

answered Mar 6, 2017 at 18:43

Usman

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11 Comments

Effy Sille Over a year ago

This is my Trailer Model class. I have it int?

public class Trailer     {         public int trailerID { get; set; }          public int? DriverID { get; set; }         public virtual Driver Driver { get; set; }     }

Effy Sille Over a year ago

It was like this from the beginning. I had it from before. It doesnot help

Usman Over a year ago

you are using Driver.driverID in code so it should be in driver class

Effy Sille Over a year ago

but driverID in Driver class is a primary key

Usman Over a year ago

are you using view model or domain model?

|

Marthijn · Accepted Answer · 2020-04-02 18:41:56Z

1

When using the Tag Helpers in ASP.NET Core the following snippet might help:

<select asp-for="DriverId" asp-items="DriverIdList" class="form-control">
  <option value="">-- please select --</option>
</select>

Note the value="", without this attribute modelbinding will fail to bind to a nullable int.

answered Apr 2, 2020 at 18:41

Marthijn

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Comments

Larry · Accepted Answer · 2022-10-06 00:53:33Z

0

You can also use the asp-for tag helper with a SelectListItem list

Then this is what you write in your form in the view

<select asp-for="(Whatever the value is associated to)" asp-items="The List<SelectListItem> list">
    <option disabled selected>---Select---</option> 
<!-- This line will go to the top of the dropdown list -->
</select>

This will create a dropdown list where by default nothing is selected and this default value will be null

You can also refer to this other post on stack overflow:

Set Default/Null Value with Select TagHelper

answered Oct 6, 2022 at 0:53

Larry

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