Question

I’ve based myself upon this question to create a custom validation attribute with asp.net mvc3 and jquery validate :

I’ve updated it to work with a group of string properties instead of bool. Which works fine. But my issue comes when I use it with custom ErrorMessage the custom message is not displayed. And I cannot figure out why.

[RequiredOneFromGroup("PhoneGroup", 
    ErrorMessageResourceName = "PhoneGroup", 
    ErrorMessageResourceType = typeof(WizardStrings))]
public String Mobile { get; set; } 
[RequiredOneFromGroup("PhoneGroup", 
    ErrorMessageResourceName = "PhoneGroup", 
    ErrorMessageResourceType = typeof(WizardStrings))]
public String Phone { get; set; }

Here’s the custom validation attribute :

[AttributeUsage(AttributeTargets.Property)]
public class RequiredOneFromGroup : ValidationAttribute, IClientValidatable
{
    public RequiredOneFromGroup(string groupName)
    {
        ErrorMessage = string.Format("You must select at least one value from group \"{0}\"", groupName);
        GroupName = groupName;
    }

    public string GroupName { get; private set; }

    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        foreach (var property in GetGroupProperties(validationContext.ObjectType))
        {
            var propertyValue = (string)property.GetValue(validationContext.ObjectInstance, null);
            if ( ! string.IsNullOrWhiteSpace(propertyValue))
            {
                // at least one property is true in this group => the model is valid
                return null;
            }
        }
        return new ValidationResult(FormatErrorMessage(validationContext.DisplayName));
    }

    private IEnumerable<PropertyInfo> GetGroupProperties(Type type)
    {
        return
            from property in type.GetProperties()
            where property.PropertyType == typeof(string)
            let attributes = property.GetCustomAttributes(typeof(RequiredOneFromGroup), false).OfType<RequiredOneFromGroup>()
            where attributes.Count() > 0
            from attribute in attributes
            where attribute.GroupName == GroupName
            select property;
    }

    public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
    {
        var groupProperties = GetGroupProperties(metadata.ContainerType).Select(p => p.Name);
        var rule = new ModelClientValidationRule
        {
            ErrorMessage = this.ErrorMessage
        };
        rule.ValidationType = string.Format("group", GroupName.ToLower());
        rule.ValidationParameters["propertynames"] = string.Join(",", groupProperties);
        yield return rule;
    }
}

I’ve tried to remove the manual setting of the ErrorMessage but then I would get an empty error message. How can I retrieve the value of ErrorMessageResourceName that I specify in the Named Parameters of the model ? And how can I set it so the custom validation attribute display it ?

Answer 1

In your GetClientValidationRules method replace:

var rule = new ModelClientValidationRule
{
    ErrorMessage = this.ErrorMessage
};

with:

var rule = new ModelClientValidationRule
{
    ErrorMessage = FormatErrorMessage(metadata.DisplayName)
};

Also get rid of the this.ErrorMessage = ... line in your constructor. You cannot set both the ErrorMessage and use a ErrorMessageResourceName and ErrorMessageResourceType properties of a validation attribute. Those things are mutually exclusive.