ASP.NET MVC 3 Data Annotation: Add validation dynamically

Question

I\'m new with data annotation. I\'d like to know if it possible (and how) to add some validation dynamically. It is very extensive to explain why, but I\'ve a ViewModel that rec

Answer 1

Custom Attribute:

[AttributeUsage(AttributeTargets.Property, AllowMultiple = true, Inherited = true)]
public class CustomRequiredIfAttribute : CustomAttribute
{
    private RequiredAttribute innerAttribute = new RequiredAttribute();
    public string DependentProperty { get; set; }
    public object TargetValue { get; set; }

    public CustomRequiredIfAttribute()
    {
    }

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

    public override bool IsValid(object value)
    {
        return innerAttribute.IsValid(value);
    }
}

Custom RequiredIfValidator

using System;
using System.Collections.Generic;
using System.Web.Mvc;

namespace Custom.Web.Validation
{
    public class RequiredIfValidator : DataAnnotationsModelValidator
    {
        public RequiredIfValidator(ModelMetadata metadata, ControllerContext context, CustomRequiredIfAttribute attribute)
            : base(metadata, context, attribute)
        {
        }

        public override IEnumerable GetClientValidationRules()
        {
            return base.GetClientValidationRules();
        }

        public override IEnumerable Validate(object container)
        {
            // get a reference to the property this validation depends upon
            var field = Metadata.ContainerType.GetProperty(Attribute.DependentProperty);

            if (field != null)
            {
                // get the value of the dependent property
                object value = field.GetValue(container, null);

                // compare the value against the target value
                if (this.IsEqual(value) || (value == null && Attribute.TargetValue == null))
                {
                    // match => means we should try validating this field
                    if (!Attribute.IsValid(Metadata.Model))
                    {
                        // validation failed - return an error
                        yield return new ModelValidationResult { Message = ErrorMessage };
                    }
                }
            }
        }

        private bool IsEqual(object dependentPropertyValue)
        {
            bool isEqual = false;

            if (Attribute.TargetValue != null && Attribute.TargetValue.GetType().IsArray)
            {
                foreach (object o in (Array)Attribute.TargetValue)
                {
                    isEqual = o.Equals(dependentPropertyValue);
                    if (isEqual)
                    {
                        break;
                    }
                }
            }
            else
            {
                isEqual = Attribute.TargetValue.Equals(dependentPropertyValue);
            }

            return isEqual;
        }
    }
}

Register custom DataAnnotationsModelValidatorProvider

DataAnnotationsModelValidatorProvider.RegisterAdapter(typeof(CustomRequiredIfAttribute), typeof(RequiredIfValidator));

Use this CustomRequiredIf in the ViewModel

[CustomRequiredIf("CategoryId", 3, ErrorMessageResourceName = GlobalResourceLiterals.AccountGroup_Required)]
public string AccountGroup { get; set; }