Question

It seems that when MVC validates a Model that it runs through the DataAnnotation attributes (like required, or range) first and if any of those fail it skips running the Validate method on my IValidatableObject model.

Is there a way to have MVC go ahead and run that method even if the other validation fails?

Answer 1

You can manually call Validate() by passing in a new instance of ValidationContext, like so:

[HttpPost]
public ActionResult Create(Model model) {
    if (!ModelState.IsValid) {
        var errors = model.Validate(new ValidationContext(model, null, null));
        foreach (var error in errors)                                 
            foreach (var memberName in error.MemberNames)
                ModelState.AddModelError(memberName, error.ErrorMessage);

        return View(post);
    }
}

A caveat of this approach is that in instances where there are no property-level (DataAnnotation) errors, the validation will be run twice. To avoid that, you could add a property to your model, say a boolean Validated, which you set to true in your Validate() method once it runs and then check before manually calling the method in your controller.

So in your controller:

if (!ModelState.IsValid) {
    if (!model.Validated) {
        var validationResults = model.Validate(new ValidationContext(model, null, null));
        foreach (var error in validationResults)
            foreach (var memberName in error.MemberNames)
                ModelState.AddModelError(memberName, error.ErrorMessage);
    }

    return View(post);
}

And in your model:

public bool Validated { get; set; }

public IEnumerable<ValidationResult> Validate(ValidationContext validationContext) {
    // perform validation

    Validated = true;
}