Add default first option as select element when populating select options from an enum field in ASP.NET Core

Question

enum field is defined as:

public enum HasSomething
{
    Installed_by_Installer,
    Not_Installed_by_Installer,
    Not_Present
}

I'm trying to add this to options in a select element as following:

<select asp-for="HasSomething" asp-items="Html.GetEnumSelectList<HasSomething>()" class="form-control">
    <option selected hidden>---Select---</option>
</select> 

The first option ---Select--- is missing out. So first value Installed by Installer automatically becomes the selected value on post which is obviously a wrong input. Can someone please guide how to overcome this problem?

Thanks in advance.

Answer 1

To make this work it's necessary to define your model property to be nullable and set it to null.

Let say the view model is declared like:

public class MyModel
{     
    public HasSomething? Something { get; set; } 
}

Then in the view use:

@model MyModel

<select class="form-control"
        asp-for="Something"
        asp-items="@Html.GetEnumSelectList<HasSomething>()">
    <option selected>---Select---</option>
</select>

Perhaps you need to add the <Nullable> directive to the project file:

<PropertyGroup>
 <Nullable>enable</Nullable>
  ...   
</PropertyGroup>

---

Another solution is to use the Display attribute and add an additional option to the enum values. Then not necessary to define the <option selected>---Select---</option>. The Unassigned value might be set by default.

public enum HasSomething
{
    [Display(Name = "---Select---")]
    Unassigned,
    [Display(Name = "Installed by Installer")]
    Installed_by_Installer,
    [Display(Name = "Not Installed by Installer")]
    Not_Installed_by_Installer,
    [Display(Name = "Not Present")]
    Not_Present
}

public class MyModel
{     
    public HasSomething? Something { get; set; } = HasSomething.Unassigned;
}