Client-side validation for custom ValidationAttrib

Question

Is it possible to implement client-site validation for custom ValidationAttribute, which is used in Class scope? For example my MaxLengthGlobal, which should assure global max limit for all input fields.

[AttributeUsage(AttributeTargets.Class)]
public class MaxLengthGlobalAttribute : ValidationAttribute, IClientValidatable
{
    public int MaximumLength
    {
        get;
        private set;
    }

    public MaxLengthGlobalAttribute(int maximumLength)
    {
        this.MaximumLength = maximumLength;
    }

    public override bool IsValid(object value)
    {
        var properties = TypeDescriptor.GetProperties(value);

        foreach (PropertyDescriptor property in properties)
        {
            var stringValue = property.GetValue(value) as string;

            if (stringValue != null && (stringValue.Length > this.MaximumLength))
            {
                return false;
            }
        }

        return true;
    }

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

        rule.ValidationParameters.Add("maxlength", this.MaximumLength);         
        yield return rule;
    }
}

Thank you.

Answer 1

Nope, it's not possible. Sorry.

Answer 2

I found this answer while looking for a solution to the same problem, and came up with a workaround.

Instead of 1 ValidationAttribute, have 2:

1.) A ServerValidationAttribute will be on the class, and will not implement IClientValidatable.

[AttributeUsage(AttributeTargets.Class, AllowMultiple = false, Inherited = true)]
public class MyCustomServerValidationAttribute : ValidationAttribute
{
    public override bool IsValid(object value)
    {
        // remember to cast to the class type, not property type
        // ... return true or false
    }
}

2.) A ClientValidationAttribute will be on the field / property, and will implement IClientValidatable, but the IsValid override always returns true.

[AttributeUsage(AttributeTargets.Field | AttributeTargets.Property, 
    AllowMultiple = false, Inherited = true)]
public class MyCustomClientValidationAttribute : ValidationAttribute, 
    IClientValidatable
{
    public override bool IsValid(object value)
    {
        return true;
    }

    public IEnumerable<ModelClientValidationRule> GetClientValidationRules(
        ModelMetadata metadata, ControllerContext context)
    {
        var rule = new ModelClientValidationRule
        {
            ErrorMessage = ErrorMessage,
            ValidationType = "mycustomvalidator",
        };

        var viewContext = (ViewContext)context;
        var dependentProperty1 = viewContext.ViewData.TemplateInfo
            .GetFullHtmlFieldId("DependentProperty1");
        //var prefix = viewContext.ViewData.TemplateInfo.HtmlFieldPrefix;

        rule.ValidationParameters.Add("dependentproperty1", dependentProperty1);

        yield return rule;
    }
}

When executed on the client, the server attribute is ignored, and vice versa.

If you need to have a validation attribute on the class, chances are the validation happens against multiple fields. I dropped in some boilerplate code for passing additional parameters to the client validation method, but it's not working as I expected. In my actual code I have commented out the viewContext and dependentProperty1 vars, and just passed a "DependentProperty1" string to the second argument of the rule.ValidationParameters.Add method. For some reason, I'm getting an incorrect HtmlFieldPrefix. If anyone can help with this please comment...

Anyway, you end up with a viewmodel like this:

[MyCustomServerValidation(ErrorMessage = MyCustomValidationMessage)]
public class MyCustomViewModel
{
    private const string MyCustomValidationMessage = "user error!";

    [Display(Name = "Email Address")]
    [MyCustomClientValidation(ErrorMessage = MyCustomValidationMessage)]
    public string Value { get; set; }

    [HiddenInput(DisplayValue = false)]
    public string DependentProperty1 { get; set; }
}

A client script like this:

/// <reference path="jquery-1.6.2.js" />
/// <reference path="jquery.validate.js" />
/// <reference path="jquery.validate.unobtrusive.js" />

$.validator.addMethod('mycustomvalidator', function (value, element, parameters) {
    var dependentProperty1 = $('#' + parameters['dependentproperty1']).val();
    // return true or false
});
$.validator.unobtrusive.adapters.add('mycustomvalidator', ['dependentproperty1'], 
    function (options) {
        options.rules['mycustomvalidator'] = {
            dependentproperty1: options.params['dependentproperty1']
        };
        options.messages['mycustomvalidator'] = options.message;
    }
);

And a view like this:

@Html.EditorFor(m => m.Value)
@Html.EditorFor(m => m.DependentProperty1)
@Html.ValidationMessageFor(m => m.Value)
@Html.ValidationMessageFor(m => m)

Then if you have client validation disabled, the @Html.ValidationMessageFor(m => m) is displayed instead of the one for the property.