Checking if model state is valid against a value in MVC

Question

I have a dropdown list in my MVC application which is a required field in my form.

I have created and filled out my list like so:

   @Html.DropDownListFor(x => x.ServiceName,
                    new SelectList(
                        new List<Object>
                        {
                            new { value = "Empty", text = "Select..."},
                            new { value = "Service Name 1", text = "Service Name 1"},
                            new { value = "Service Name 1", text = "Service Name 2"},
                            new { value = "Service Name 1", text = "Service Name 3"},
                            new { value = "Service Name 1", text = "Service Name 4"}
                        },
                            "value",
                            "text",
                            0), new { @class = "form-control" })

I'm needing my form to return back a message that tells the user that they need to select an option from this menu is they do no select anything. My service name has [Required(ErrorMessage = "Service Name must be selected")] above it in my Model class.

It looks like this:

[Required(ErrorMessage = "Service Name must be selected")]
public string ServiceName { get; set; }

However I have no idea how I can check against this value. So far I've tried the following:

if(newMember.getProperty("serviceManager").Value == "0")
{
   ModelState.IsValid = false;
}

But this doesn't work. I've tried a few variations of the above but they haven't worked either. Im currently googling to find an answer but I'm not having much luck.

Could someone please explain to me how I can achieve what I want to achieve?

Edit

Just updated my code to show the new test I just completed but it still didn't return back an error telling me Service must be selected when I submit an empty form.

Answer 1

Use the overload of DropDownListFor() that renders an option label, and make you ServiceName property nullable with [Required] attribute. The issue with you existing SelectList is that you include the first option which has a value ("Empty") which is a valid string so it passes validation.

Model

[Required]
public string ServiceName { get; set; }

Controller

List<string> services = new List<string>() { "Service Name 1", "Service Name 2", "Service Name 3", "Service Name 4" };
ViewBag.Services = new SelectList(services);
return View(yourModel);

View

@Html.DropDownListFor(x => x.ServiceName, (SelectList)ViewBag.Services, "--Please Select--", new { @class = "form-control" })
@Html.ValidationMessagFor(x => x.ServiceName)

Note the SelectList does not contain an element for "--Please Select--". The 3rd parameter of DropDownListFor() adds a label option which has no value <option value>--Please Select--</option> which if selected will result in the property being invalid.

Answer 2

You have your getProperty to get serviceManager but you view is binding to ServiceName.

Try changing it to...

if(newMember.getProperty("ServiceName").Value == "0")

OR

I dont have visual studio available at the minute so code might not be exact.

@Html.DropDownListFor(x => x.ServiceName,
                new SelectList(
                    new List<Object>
                    {
                        new { value = 1, text = "Service Name 1"},
                        new { value = 2, text = "Service Name 2"},
                        new { value = 3, text = "Service Name 3"},
                        new { value = 4, text = "Service Name 4"}
                    },
                        "value",
                        "text",
                        0), "Select...", new { @class = "form-control" })

and if you have [Required] on your ServiceName in your ViewModel then in your controller you will be able to do ModelState.IsValid e.g.

if(ModelState.IsValid){
    // Do code here if it is valid
}else{
    return View(viewModel)
}