Asp.Net MVC Validation - dependent fields

Question

I'm currently trying to work through MVC validation, and am coming up against some problems where a field is required depending on the value of another field. An example is below (that I haven't figured out yet) - If the PaymentMethod == "Cheque", then the ChequeName should be required, otherwise it can be let through.

[Required(ErrorMessage = "Payment Method must be selected")]
public override string PaymentMethod
{ get; set; }

[Required(ErrorMessage = "ChequeName is required")]
public override string ChequeName
{ get; set; }

I'm using the System.ComponentModel.DataAnnotations for the [Required], and have also extended a ValidationAttribute to try and get this working, but I can't pass a variable through to do the validation (extension below)

public class JEPaymentDetailRequired : ValidationAttribute 
{
    public string PaymentSelected { get; set; }
    public string PaymentType { get; set; }

    public override bool IsValid(object value)
    {
        if (PaymentSelected != PaymentType)
            return true;
        var stringDetail = (string) value;
        if (stringDetail.Length == 0)
            return false;
        return true;
    }
}

Implementation:

[JEPaymentDetailRequired(PaymentSelected = PaymentMethod, PaymentType = "Cheque", ErrorMessage = "Cheque name must be completed when payment type of cheque")]

Has anyone had experience with this sort of validation? Would it just be better to write it into the controller?

Thanks for your help.

Answer 1

If you want client side validation in addition to model validation on the server, I think the best way to go is a custom validation attribute (like Jaroslaw suggested). I'm including the source here of the one I use.

Custom attribute:

public class RequiredIfAttribute : DependentPropertyAttribute
{
    private readonly RequiredAttribute innerAttribute = new RequiredAttribute();

    public object TargetValue { get; set; }


    public RequiredIfAttribute(string dependentProperty, object targetValue) : base(dependentProperty)
    {
        TargetValue = targetValue;
    }


    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        // get a reference to the property this validation depends upon
        var containerType = validationContext.ObjectInstance.GetType();
        var field = containerType.GetProperty(DependentProperty);

        if (field != null)
        {
            // get the value of the dependent property
            var dependentvalue = field.GetValue(validationContext.ObjectInstance, null);

            // compare the value against the target value
            if ((dependentvalue == null && TargetValue == null) ||
                (dependentvalue != null && dependentvalue.Equals(TargetValue)))
            {
                // match => means we should try validating this field
                if (!innerAttribute.IsValid(value))
                    // validation failed - return an error
                    return new ValidationResult(ErrorMessage, new[] { validationContext.MemberName });
            }
        }

        return ValidationResult.Success;
    }

    public override IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
    {
        var rule = new ModelClientValidationRule
                       {
                           ErrorMessage = FormatErrorMessage(metadata.GetDisplayName()),
                           ValidationType = "requiredif"
                       };

        var depProp = BuildDependentPropertyId(DependentProperty, metadata, context as ViewContext);

        // find the value on the control we depend on;
        // if it's a bool, format it javascript style 
        // (the default is True or False!)
        var targetValue = (TargetValue ?? "").ToString();
        if (TargetValue != null)
            if (TargetValue is bool)
                targetValue = targetValue.ToLower();

        rule.ValidationParameters.Add("dependentproperty", depProp);
        rule.ValidationParameters.Add("targetvalue", targetValue);

        yield return rule;
    }
}

Jquery validation extension:

$.validator.unobtrusive.adapters.add('requiredif', ['dependentproperty', 'targetvalue'], function (options) {
    options.rules['requiredif'] = {
        dependentproperty: options.params['dependentproperty'],
        targetvalue: options.params['targetvalue']
    };
    options.messages['requiredif'] = options.message;
});

$.validator.addMethod('requiredif',
    function (value, element, parameters) {
        var id = '#' + parameters['dependentproperty'];

        // get the target value (as a string, 
        // as that's what actual value will be)
        var targetvalue = parameters['targetvalue'];
        targetvalue = (targetvalue == null ? '' : targetvalue).toString();

        // get the actual value of the target control
        var actualvalue = getControlValue(id);

        // if the condition is true, reuse the existing 
        // required field validator functionality
        if (targetvalue === actualvalue) {
            return $.validator.methods.required.call(this, value, element, parameters);
        }

        return true;
    }
);

Decorating a property with the attribute:

[Required]
public bool IsEmailGiftCertificate { get; set; }

[RequiredIf("IsEmailGiftCertificate", true, ErrorMessage = "Please provide Your Email.")]
public string YourEmail { get; set; }