Validate checkbox on the client with FluentValidation/MVC 3

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 v

Answer 1

I am coding in ASP.NET MVC5 and Darin's code produces a javascript error on the lines that reference value.ToLowerCase() when a checkbox is involved. Another issue is that this code invalidates the client side equality comparison between two properties. It only seems to work when comparing against a literal value...That may have been his intent, but I need it to work for both situations:

Here's one possible workaround, that involves only two changes to Darin's answer:

First, I updated the javascript function with the following.

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

Secondly, I updated EqualToValueFluentValidationPropertyValidator with the following:

public class EqualToValueFluentValidationPropertyValidator : FluentValidationPropertyValidator
{
    EqualValidator EqualValidator 
    {
        get { return (EqualValidator)Validator; }
    }

    public EqualToValueFluentValidationPropertyValidator(ModelMetadata metadata, ControllerContext controllerContext, PropertyRule rule, IPropertyValidator validator) : base(metadata, controllerContext, rule, validator) {
        ShouldValidate = false;
    }

    public override IEnumerable GetClientValidationRules() {
        if (!ShouldGenerateClientSideRules()) yield break;

        var propertyToCompare = EqualValidator.MemberToCompare as PropertyInfo;
        if(propertyToCompare != null) {
            // If propertyToCompare is not null then we're comparing to another property.
            // If propertyToCompare is null then we're either comparing against a literal value, a field or a method call.
            // We only care about property comparisons in this case.

            var comparisonDisplayName =
                ValidatorOptions.DisplayNameResolver(Rule.TypeToValidate, propertyToCompare, null)
                ?? propertyToCompare.Name.SplitPascalCase();

            var formatter = new MessageFormatter()
                .AppendPropertyName(Rule.GetDisplayName())
                .AppendArgument("ComparisonValue", comparisonDisplayName);


            string message = formatter.BuildMessage(EqualValidator.ErrorMessageSource.GetString());
            yield return new ModelClientValidationEqualToRule(message, CompareAttribute.FormatPropertyForClientValidation(propertyToCompare.Name)) ;
        }
        else
        {
            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;
        }
    }
}

This code was copied from the EqualToFluentValidationPropertyValidator internal class in the fluentvalidation source, and I added Darin's logic after the else. This allows the client-side validation to work for property comparisons as well as value comparisons...I'm not sure if this is a great approach since you're basically overriding the built-in equality validator and it may break in future releases of fluent validation....but Darin's answer has the same issue.

There might be better ways to handle this. If somebody knows of a way to directly include the logic from the internal EqualToFluentValidationPropertyValidator class, then I'd love to hear it.