How to access ModelState.AddModelError() from IsValid function of ValidationAttribute class

Question

i try to add this line ModelState.AddModelError(string key, string errorMessage); in IsValid function of ValidationAttribute class but fail.

[AttributeUsage(AttributeTargets.Property, AllowMultiple = true, Inherited = true)]
    public class AtleastOneAttribute : ValidationAttribute, IClientValidatable
    {
        // For Server side
        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            if (value != null)
            {
                var oHobby=value as IEnumerable;

                foreach (var _object in oHobby)
                {
                    Hobby _oHobby = (Hobby)_object;
                    if (_oHobby.IsSelected)
                    {
                        return ValidationResult.Success;
                    }
                }

            }
             ModelState.AddModelError("Hobbies", "Err message....");

            return new ValidationResult(FormatErrorMessage(validationContext.DisplayName));
        }

tell me how to access ModelState.AddModelError from IsValid function of ValidationAttribute class ?

thanks

Answer 1

ModelState is not accessible in IsValid function. IsValid method adds an error to ModelState through it's return statement, so if you need to add an error just return it:

return new ValidationResult("Err message....");