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asp.net-mvcvalidationhtml.dropdownlistfordatamodel

How to create ASP.Net MVC DropDownList with required validation

I working with mvc 5. I am loading data from Database Using ORM and fill a drop down list from the controller, like this.

ViewBag.Country_id = new SelectList(_db.Countries, "Country_id", "Description");

As i wanted an empty field first I am doing this in my HTML.

<div class="form-group">
    @Html.LabelFor(model => model.Countries, "Country", htmlAttributes: new { @class = "control-label col-md-2" })
    <div class="col-md-10">
        @Html.DropDownList("Country_id", null, htmlAttributes: new { @class = "form-control" }, optionLabel: "Choose a Country")
        @Html.ValidationMessageFor(model => model.Country_id, "", new { @class = "text-danger" })
    </div>
</div>

The empty choice has a "0" value.

And i wanted to validate the user choose a Country so I add this Validation

[Required,Range(1, int.MaxValue, ErrorMessage = "Error: Must Choose a Country")]
public int Country_id { get; set; }

The Problem is that never get me a Error. Always is "0" and the validation did not occur.

What I a missing?

Solution

  • There are few ways to work with DropDownList. I personally like to use Strongly-Type ViewModel instead of ViewBag.

    Screen Shot

    Validation message displays when submit button is clicked without selecting Country.

    enter image description here

    Entity

    public class Country
{
    public int Country_id { get; set; }
    public string Description { get; set; }
}

    Model

    public class CountryViewModel
{
    [Display(Name = "Country")]
    [Required(ErrorMessage = "{0} is required.")]
    public int SelectedCountryId { get; set; }

    public IList<SelectListItem> AvailableCountries { get; set; }

    public CountryViewModel()
    {
        AvailableCountries = new List<SelectListItem>();
    }
}

    Controller

    public class HomeController : Controller
{
    public ActionResult Create()
    {
        var countries = GetCountries();
        var model = new CountryViewModel {AvailableCountries = countries};
        return View(model);
    }

    [HttpPost]
    public async Task<ActionResult> Create(CountryViewModel countryViewModel)
    {
        if (ModelState.IsValid)
        {
            int countryId = countryViewModel.SelectedCountryId;
            // Do something
        }
        // If we got this far, something failed. So, redisplay form
        countryViewModel.AvailableCountries = GetCountries();
        return View(countryViewModel);
    }

    public IList<SelectListItem> GetCountries()
    {
        // This comes from database.
        var _dbCountries = new List<Country>
        {
            new Country {Country_id = 1, Description = "USA"},
            new Country {Country_id = 2, Description = "UK"},
            new Country {Country_id = 3, Description = "Canada"},
        };
        var countries = _dbCountries
            .Select(x => new SelectListItem {Text = x.Description, Value = x.Country_id.ToString()})
            .ToList();
        countries.Insert(0, new SelectListItem {Text = "Choose a Country", Value = ""});
        return countries;
    }
}

    View

    @model DemoMvc.Models.CountryViewModel
@{
    Layout = null;
}

<!DOCTYPE html>

<html>
<head>
    <meta name="viewport" content="width=device-width" />
    <title>Create</title>
</head>
<body>

    <h2>Create</h2>

    @using (Html.BeginForm())
    {
        <div class="form-group">
            @Html.LabelFor(model => model.SelectedCountryId, 
               new {@class = "control-label col-md-2"})
            <div class="col-md-10">
                @Html.DropDownListFor(model => model.SelectedCountryId, 
                    Model.AvailableCountries, new {@class = "form-control"})
                @Html.ValidationMessageFor(model => model.SelectedCountryId, 
                     "", new {@class = "text-danger"})
            </div>
        </div>

        <input type="submit" value="Submit"/>
    }

</body>
</html>