在Asp.Net MVC中实现RequiredIf标签对Model中的属性进行验证

在Asp.Net MVC中可以用继承ValidationAttribute的方式，自定制实现RequiredIf标签对Model中的属性进行验证

具体场景为：某一属性是否允许为null的验证，要根据另一个属性值是否为true来判断

代码如下所示：

1）：后台代码

    public class RequiredIfAttribute : ValidationAttribute, IClientValidatable
    {
        private RequiredAttribute innerAttribute = new RequiredAttribute();
        public string DependentProperty { get; set; }
        public object TargetValue { get; set; }

        public RequiredIfAttribute(string dependentProperty, object targetValue)
        {
            this.DependentProperty = dependentProperty;
            this.TargetValue = targetValue;
        }

        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            var field = validationContext.ObjectInstance.GetType().GetProperty(DependentProperty);
            if (field != null)
            {
                var dependentValue = field.GetValue(validationContext.ObjectInstance, null);
                if (Object.Equals(dependentValue, TargetValue))
                {
                    if (!innerAttribute.IsValid(value))
                        return new ValidationResult(ErrorMessage);
                }
            }
            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;
        }

    }

2）：前台代码

$.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);
    if (control == null || control.length == 0) { // if control is null, the control is a checkbox or a radio
        control = $("[name='" + parameters['dependentproperty'] + "']:checked");
    }
    var controltype = control.attr('type');
    var actualvalue =
        (controltype === 'checkbox' || controltype === 'radio') ?
        control.val() != "" ? control.val() : control.prop('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;
});

将标签RequiredIf添加到对应的属性上

【注：第一个参数为相关联的属性名，第二个参数表示相关联属性值（相关联属性值=第二个参数时，再对此属性进行验证），第三个参数为错误提示信息】

        public class EricSunModel
        {
            public bool ContainsDangerousGoods { get; set; }

            [RequiredIf("ContainsDangerousGoods", true, ErrorMessage = "Please enter UN Number")]
            [Display(Name = "UN Number")]
            public string UNNumber { get; set; }
        }

更多细节请参考如下链接：

http://mvcdiary.com/2013/02/28/conditional-required-validation-or-field-mandatory-depends-on-another-field-mvc-4/