ASP.NET MVC custom multiple fields validation

Question

I'm developing an ASP.NET MVC 5.2.3 custom data annotation for validation in Visual Studio 2015. It needs to take any number of fields and ensure that if one has a value, they all must have a value; if they're all null/blank, it should be okay.

A few examples have helped:

• ASP.NET MVC implement custom validator use IClientValidatable
• MVC Form Validation on Multiple Fields
• http://www.macaalay.com/2014/02/24/unobtrusive-client-and-server-side-age-validation-in-mvc-using-custom-data-annotations/

However, I'm not sure how to do the client-side validation where you have an unknown number of fields being validated.

How do you pass that to the client using the implementation of the GetClientValidationRules() method of the IClientValidatable interface?

Also, how do I apply this new data annotation to the properties on my view model? Would it look like this?

[MultipleRequired("AppNumber", "UserId", /* more fields */), ErrorMessage = "Something..."]
[DisplayName("App #")]
public int AppNumber { get; set; }

[DisplayName("User ID")]
public int UserId { get; set; }

Here's as far as I could get with the MultipleRequiredAttribute custom data annotation class:

public class MultipleRequiredAttribute : ValidationAttribute, IClientValidatable
{
    private readonly string[] _fields;
    public MultipleRequiredAttribute(params string[] fields)
    {
        _fields = fields;
    }

    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        // If any field has value, then all must have value
        var anyHasValue = _fields.Any(f => !string.IsNullOrEmpty(f));

        if (!anyHasValue) return null;

        foreach (var field in _fields)
        {
            var property = validationContext.ObjectType.GetProperty(field);
            if (property == null)
                return new ValidationResult($"Property '{field}' is undefined.");

            var fieldValue = property.GetValue(validationContext.ObjectInstance, null);

            if (string.IsNullOrEmpty(fieldValue?.ToString()))
                return new ValidationResult(FormatErrorMessage(validationContext.DisplayName));
        }

        return null;
    }

    public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
    {
        yield return new ModelClientValidationRule
        {
            ErrorMessage = ErrorMessage,
            ValidationType = "multiplerequired"
        };
    }
}

Thank you.

Answer 1

In order to get client side validation, you need to pass the values of the 'other properties' in the ModelClientValidationRule by using the .Add() method of the rules ValidationParameters property, and then write the client side scripts to add the rules to the $.validator.

But first there are a few other issues to address with your attribute. First you should execute your foreach loop only if the value of the property you applied the attribute is null. Second, returning a ValidationResult if one of the 'other properties' does not exist is confusing and meaningless to a user and you should just ignore it.

The attribute code should be (note I changed the name of the attribute)

public class RequiredIfAnyAttribute : ValidationAttribute, IClientValidatable
{
    private readonly string[] _otherProperties;
    private const string _DefaultErrorMessage = "The {0} field is required";

    public RequiredIfAnyAttribute(params string[] otherProperties)
    {
        if (otherProperties.Length == 0) // would not make sense
        {
            throw new ArgumentException("At least one other property name must be provided");
        }
        _otherProperties = otherProperties;
        ErrorMessage = _DefaultErrorMessage;
    }

    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        if (value == null) // no point checking if it has a value
        {
            foreach (string property in _otherProperties)
            {
                var propertyName = validationContext.ObjectType.GetProperty(property);
                if (propertyName == null)
                {
                    continue;
                }
                var propertyValue = propertyName.GetValue(validationContext.ObjectInstance, null);
                if (propertyValue != null)
                {
                    return new ValidationResult(FormatErrorMessage(validationContext.DisplayName));
                }
            }
        }
        return ValidationResult.Success;
    }
    public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
    {
        var rule = new ModelClientValidationRule
        {
            ValidationType = "requiredifany",
            ErrorMessage = FormatErrorMessage(metadata.GetDisplayName()),
        };
        / pass a comma separated list of the other propeties
        rule.ValidationParameters.Add("otherproperties", string.Join(",", _otherProperties));
        yield return rule;
    }
}

The scripts will then be

sandtrapValidation = {
    getDependentElement: function (validationElement, dependentProperty) {
        var dependentElement = $('#' + dependentProperty);
        if (dependentElement.length === 1) {
            return dependentElement;
        }
        var name = validationElement.name;
        var index = name.lastIndexOf(".") + 1;
        var id = (name.substr(0, index) + dependentProperty).replace(/[\.\[\]]/g, "_");
        dependentElement = $('#' + id);
        if (dependentElement.length === 1) {
            return dependentElement;
        }
        // Try using the name attribute
        name = (name.substr(0, index) + dependentProperty);
        dependentElement = $('[name="' + name + '"]');
        if (dependentElement.length > 0) {
            return dependentElement.first();
        }
        return null;
    }
}

$.validator.unobtrusive.adapters.add("requiredifany", ["otherproperties"], function (options) {
    var element = options.element;
    var otherNames = options.params.otherproperties.split(',');
    var otherProperties = [];
    $.each(otherNames, function (index, item) {
        otherProperties.push(sandtrapValidation.getDependentElement(element, item))
    });
    options.rules['requiredifany'] = {
        otherproperties: otherProperties
    };
    options.messages['requiredifany'] = options.message;
});

$.validator.addMethod("requiredifany", function (value, element, params) {
    if ($(element).val() != '') {
        // The element has a value so its OK
        return true;
    }
    var isValid = true;
    $.each(params.otherproperties, function (index, item) {
        if ($(this).val() != '') {
            isValid = false;
        }
    });
    return isValid;
});