ASP.NET MVC models that can be validated without using attributes

Question

The model looks like this, with no attributes:

public class PersonalModel : Validatable
{ 
 public string Name { get; set; } 
 public string Email { get; set; }
 public override void Validate(dynamic item)
 {
 if (this.ValidatesPresenceOf(item.Name, "Name is required"))
 { 
 if (((String)item.Name).Length > 5)
 {
 Errors.Add("name is too long less than 5 chars please!");
 }
 } 
 } 
}

and the action looks like this:

 [HttpPost]
 [ValidateAntiForgeryToken]
 public ActionResult PersonalInfo(PersonalModel model)
 {
 if (model.IsValid(model))
 {
 this.FlashInfo("Your Personal info was successfully received");
 return RedirectToAction("ThankYou");
 }
 else
 { 
 ModelState.AddModelError(string.Empty, String.Join("; ", model.Errors.ToArray())) ; 
 return View(model);
 }
 }

This is the baseclass Validatable:

public class Validatable : DynamicObject
{
 //Hooks
 public virtual void Validate(dynamic item) { }
 //Temporary holder for error messages
 public IList<string> Errors = new List<string>();
 public bool IsValid(dynamic item)
 {
 Errors.Clear();
 Validate(item);
 return Errors.Count == 0;
 }
 //validation methods
 public virtual bool ValidatesPresenceOf(object value, string message = "Required")
 {
 if (value == null || String.IsNullOrEmpty(value.ToString())) 
 {
 Errors.Add(message);
 return false;
 }
 return true;
 }
}

Answer 1

I wholeheartedly agree that the attributes are evil. But in my opinion having to derive from a base class is just as bad as having to add attributes. Both makes you depend on framework infrastructure you don't need to depend on. (Models should be model logic, and model logic only.)

In MVC (3 at least) you can implement a ModelValidatorProvider and a ModelMetadataProvider. The validator provider can be added in Application_Start using ModelValidatorProviders.Providers.Add(...), and the metdata provider can be injected using the standard IoC container.

The guys who wrote Professional ASP.NET MVC 3 also created fluent implementations of those, so you can have configuration like this:

validationProvider.ForModel<PersonModel>()
 .ForProperty(p => p.Name).Required()
 .ForProperty(p => p.Email).Required().Email();

This will also be picked up by the unobtrusive validation jQuery plugin, and everything else in MVC that would've used the attributes for.

As a sidenote, since you also derive from DynamicObject in your base class, the compiler won't complain if someone inadvertedly attempts to set person.name instead of person.Name.

• eiu165: Looking at this again I agree with your thoughts 'having to derive from a base class is just as bad as having to add attributes' Thanks Lars-Erik