Question

I am trying to validate if a check box is checked on the client using FluentValidation. I can’t figure it our for the life of me.

Can it be done using unobtrusive validation?

Answer 1

Let’s assume that you have the following model:

[Validator(typeof(MyViewModelValidator))]
public class MyViewModel
{
    public bool IsChecked { get; set; }
}

with the following validator:

public class MyViewModelValidator : AbstractValidator<MyViewModel>
{
    public MyViewModelValidator()
    {
        RuleFor(x => x.IsChecked).Equal(true).WithMessage("Please check this checkbox");
    }
}

and a controller:

public class HomeController : Controller
{
    public ActionResult Index()
    {
        return View();
    }

    [HttpPost]
    public ActionResult Index(MyViewModel model)
    {
        return View(model);
    }
}

with a corresponding view:

@model MyViewModel
@using (Html.BeginForm())
{
    @Html.LabelFor(x => x.IsChecked)
    @Html.CheckBoxFor(x => x.IsChecked)
    @Html.ValidationMessageFor(x => x.IsChecked)
    <button type="submit">OK</button>
}

and in Global.asax you have registered the fluent validation model validator provider:

FluentValidationModelValidatorProvider.Configure();

So far we have server side validation up and running fine. That’s good. That’s always the first part that we must setup. I have seen people focusing too much on doing client side validation that they forget doing server side validation and when you disable javascript (or even worse if you stumble upon a user with bad intentions), well, bad things happen.
So far we are confident because we know that even if something gets screwed up on the client our domain is protected with server side validation.

---

So let’s now take care for the client validation. Out of the box FluentValidation.NET supports automatic client validation for the EqualTo validator but when comparing against another property value which is the equivalent of the [Compare] data annotation.

But in our case we are comparing against a fixed value. So we don’t get client side vaildation out of the box. And when we don’t get something out of the box, we need to put it in the box.

So we start by defining a custom FluentValidationPropertyValidator:

public class EqualToValueFluentValidationPropertyValidator : FluentValidationPropertyValidator
{
    public EqualToValueFluentValidationPropertyValidator(ModelMetadata metadata, ControllerContext controllerContext, PropertyRule rule, IPropertyValidator validator)
        : base(metadata, controllerContext, rule, validator)
    {
    }

    public override IEnumerable<ModelClientValidationRule> GetClientValidationRules()
    {
        if (!this.ShouldGenerateClientSideRules())
        {
            yield break;
        }
        var validator = (EqualValidator)Validator;

        var errorMessage = new MessageFormatter()
            .AppendPropertyName(Rule.GetDisplayName())
            .AppendArgument("ValueToCompare", validator.ValueToCompare)
            .BuildMessage(validator.ErrorMessageSource.GetString());

        var rule = new ModelClientValidationRule();
        rule.ErrorMessage = errorMessage;
        rule.ValidationType = "equaltovalue";
        rule.ValidationParameters["valuetocompare"] = validator.ValueToCompare;
        yield return rule;
    }
}

that we are going to register in Application_Start:

FluentValidationModelValidatorProvider.Configure(provider =>
{
    provider.AddImplicitRequiredValidator = false;
    provider.Add(typeof(EqualValidator), (metadata, context, description, validator) => new EqualToValueFluentValidationPropertyValidator(metadata, context, description, validator));
});

So far we have associated our custom FluentValidationPropertyValidator with the EqualValidator.

The last part is to write a custom adapter:

(function ($) {
    $.validator.unobtrusive.adapters.add('equaltovalue', ['valuetocompare'], function (options) {
        options.rules['equaltovalue'] = options.params;
        if (options.message != null) {
            options.messages['equaltovalue'] = options.message;
        }
    });

    $.validator.addMethod('equaltovalue', function (value, element, params) {
        if ($(element).is(':checkbox')) {
            if ($(element).is(':checked')) {
                return value.toLowerCase() === 'true';
            } else {
                return value.toLowerCase() === 'false';
            }
        }
        return params.valuetocompare.toLowerCase() === value.toLowerCase();
    });
})(jQuery);    

And that’s pretty much it. All that’s left is to include the client scripts:

<script src="@Url.Content("~/Scripts/jquery.validate.js")" type="text/javascript"></script>
<script src="@Url.Content("~/Scripts/jquery.validate.unobtrusive.js")" type="text/javascript"></script>
<script src="@Url.Content("~/Scripts/customadapter.js")" type="text/javascript"></script>