custom attribute to set string lenght dynamically

Question

HI,

I want to set a string lenght for particular property by using custom attribute,i dnt want to set a constant string lenght

[Required(ErrorMessageResourceType = typeof(CampaignResource.VendorCampaign), ErrorMessageResourceName = "TitleRequired")]

[CustomValidation(typeof(VendorCampaignValidator), "ValidateName")]

[Display(Name = "Title", ResourceType = typeof(CampaignResource.VendorCampaign))]

public string Title { get; set; }///

public class VendorCampaignValidator : ValidationAttribute

{

public static ValidationResult ValidateName(string campaignName)

{

ResourceManager rm = new ResourceManager(typeof(InQuest.Sax.Resources.VendorCampaign));

if (string.IsNullOrWhiteSpace(campaignName))

return new ValidationResult(rm.GetString("TitleRequired"));

if (campaignName.Length <= VendorCampaignSettings.NameMaxLength)

{

return ValidationResult.Success;

}

else

{

return new ValidationResult(rm.GetString("InvalidLengthTitle"));

// return new ValidationResult(rm.GetString("Title should be at most 25 characters long"));

}

I am taking value from web.config file but it is not working