Question

Model:

using System.ComponentModel.DataAnnotations;
using MySite.Validators;

namespace MySite.Models
{
    public class AddItem
    {
        [Required(ErrorMessage = "Name is required")]
        public string Name { get; set; }

        [TagValidation(ErrorMessage = "At least one tag is required")]
        public virtual List<int> Tags { get; set; }
    }
}

View:

@using (Html.BeginForm()) {
    ...
    <div class="editor-label">
        @Html.LabelFor(model => model.Tags, "Tags")
    </div>
    <div class="editor-field">
        @Html.ListBox("Tags")
        @Html.ValidationMessageFor(model => model.Tags)
    </div>
    ...
}

Validator:

using System.ComponentModel.DataAnnotations;

namespace MySite.Validators
{
    public class TagValidationAttribute : ValidationAttribute
    {
        public override bool IsValid(object value)
        {
            return false;
        }
    }
}

I want my validator to return false to begin with, just to make sure it’s working. However, if I don’t select any tags from the list and submit the form, it tries to process it without any errors indicating that I need to select a tag first.

What am I doing wrong here?

Answer 1

I had commented out the if (ModelState.IsValid == false) check in my controller, so I wasn’t getting any validation. The reason I did this, initially, was because I was getting an error when I tried to pass the model back to the view, because the ListBox field in the view expected a IEnumerable and not a List.

Here’s how I fixed both problems (in the controller):

[HttpPost]
public ActionResult AddItem(AddItem AddItem)
{
    if (ModelState.IsValid == false)
    {
        ModelState.AddModelError("", "Model not valid.");

        List<Tag> Tags = Db.Tags.ToList();

        ViewBag.Tags = new SelectList(Tags, "TagId", "Name");

        return View(AddItem);
    }

    //...
}