When working on .NET MVC projects you may run into a situation where you need to override the state reported by the ModelState object.  In case you aren’t familiar with what the ModelState object is, in the case of MVC controllers the ModelState object provides details on whether the data in a form sent to the controller passes all model defined attribute validation checks.  A call to ModelState.IsValid returns a boolean value to indicate the state, true for all checks passed, false for one or more errors present.  Further details on the reasons why the model is not valid can be retrieved from the ModelState.Errors collection.  In some cases it may be necessary to remove some validation errors from the ModelState before calling ModelState.IsValid.  

I recently had to do this when a complex form required a major overhaul.  Ideally we would have built new form data models but constraints on the project didn’t permit the investment.  Instead a function was created that would remove validation errors for the few form elements causing validation issues.

The function wasn’t complex.  For our needs we wanted to remove all errors against an element that contained a given name.  This was because our form would contain input elements with names like these that created a natural hierarchy and grouping:  Car.Door.Front.Passenger.Color and Car.Body.Windshield.Size.  To do this we’d check each ModelState Key to see if it contained the element name of interest.  If it did then the ModelState.Values object at the same index of the found key would have its Errors collection cleared.

public void RemoveModelStateErrors(string elementName) {
    for(var idx = 0; idx < ModelState.Keys.Count; idx++) {
        if (ModelState.Keys.ElementAt(i).Contains(elementName)
            && ModelState.Values.ElementAt(i).Errors.Count > 0) { 
            ModelState.Values.ElementAt(i).Errors.Clear();
        }
    }
}

The function could be simplified if you always know the exact element name or it could be refactored to handle a list of element names.  Either way once the function is called, any errors related to the elementName would be removed and the ModelState.IsValid call will be updated accordingly.  If the only errors were related to the elements that were just removed then it would return true for the valid model.