MVC 3 field mandatory if another field is filled

Question

I have a simple question.

I have for example two fileds mapped on model ex: textbox_1 and textbox_2.

I whant to ask if exist a way (ex mandatory decorator) that imposes textbox_2 mandatory ONLY if I fill textbox_1. IF I do not fill textbox_1 textbox 2 is optional.

Is there an elegant way to do this ?

Answer 1

There is no out of the box solution in ASP.NET MVC for this. Here is the attribute I created to solve it. There are 3 available usages for the attribute:

• Pass null as targetValue to constructor: required only when dependent field is null.
• Pass any value as tagetValue: required only when dependent field equals passed in any value.
• Pass "*" as tagetValue: required only when dependent field is populated.

In your case you need to pass "*" as targetValue to the constructor, meaning that dependent property can be any non null value.

Note: it contains both, server and client side (+ unobtrusive) validation.

Server side attribute class:

public class RequiredIfAttribute : ValidationAttribute, IClientValidatable
{
    protected RequiredAttribute _innerAttribute;

    public string DependentProperty { get; set; }
    public object TargetValue { get; set; }

    public bool AllowEmptyStrings
    {
        get
        {
            return _innerAttribute.AllowEmptyStrings;
        }
        set
        {
            _innerAttribute.AllowEmptyStrings = value;
        }
    }

    public RequiredIfAttribute(string dependentProperty, object targetValue)
    {
        _innerAttribute = new RequiredAttribute();
        DependentProperty = 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);
            // trim spaces of dependent value
            if (dependentValue != null && dependentValue is string)
            {
                dependentValue = (dependentValue as string).Trim();

                if (!AllowEmptyStrings && (dependentValue as string).Length == 0)
                {
                    dependentValue = null;
                }
            }

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

        return ValidationResult.Success;
    }

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

        string depProp = BuildDependentPropertyId(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!)
        string targetValue = (TargetValue ?? "").ToString();
        if (TargetValue is bool)
            targetValue = targetValue.ToLower();

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

        yield return rule;
    }

    private string BuildDependentPropertyId(ModelMetadata metadata, ViewContext viewContext)
    {
        // build the ID of the property
        string depProp = viewContext.ViewData.TemplateInfo.GetFullHtmlFieldId(DependentProperty);
        // unfortunately this will have the name of the current field appended to the beginning,
        // because the TemplateInfo's context has had this fieldname appended to it. Instead, we
        // want to get the context as though it was one level higher (i.e. outside the current property,
        // which is the containing object, and hence the same level as the dependent property.
        var thisField = metadata.PropertyName + "_";
        if (depProp.StartsWith(thisField))
            // strip it off again
            depProp = depProp.Substring(thisField.Length);
        return depProp;
    }
}

Client side (including unobtrusive validation):

$.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
        // note - this probably needs to cater for more 
        // control types, e.g. radios
        var control = $(id);
        var controltype = control.attr('type');
        var actualvalue =
            controltype === 'checkbox' ?
            control.attr('checked').toString() :
            control.val();

        // if the condition is true, reuse the existing 
        // required field validator functionality
        if ($.trim(targetvalue) === $.trim(actualvalue) || ($.trim(targetvalue) === '*' && $.trim(actualvalue) !== ''))
            return $.validator.methods.required.call(
              this, value, element, parameters);

        return true;
    });

$.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;
    });