Question

Given the following Model,

public class A {     public string Name { get; set; } }  public class B {     public string Address { get; set; }     public A InstanceOfA { get; set; } } 

View,

<%= Html.TextBox('A.Name') %> 

and Controller

UpdateModel<B>(b, collection.ToValueProvider()); 

my b instance will contain a property of A with an empty string for Name.

Is there anyway to have UpdateModel set the A property to null if no value has been entered for name?

To clarify, this is a simple case, my real world scenario contains data models with hundreds of properties of this ilk. The definition of these data models is out of my hands. Therefore I need a solution for the general case, ie don’t create a property if no values have been entered.

Further clarification: i need this to work in edit scenarios aswell, i.e. an instance of b with A.Name set to ‘foo’ is edited to set A.Name to ”, i want A to be null.

Answer 1

I just discovered this behavior (by accident thanks to a check constraint) and I think it is a mistake. I wonder how many devs are now inadvertently saving empty strings into their db instead of null? 🙂

Anyway, I’m going to explore this a bit more and see if there is a better solution.

Update:

Here is a solution:

using System.ComponentModel; using System.Web.Mvc;  namespace CustomerWebsite.Mvc {   public sealed class EmptyStringToNullModelBinder : DefaultModelBinder   {     protected override void SetProperty(ControllerContext controllerContext,       ModelBindingContext bindingContext, PropertyDescriptor propertyDescriptor, object value)     {       if ((value != null)           && (value.GetType() == typeof(string)               && ((string)value).Length == 0))       {         value = null;       }        base.SetProperty(controllerContext, bindingContext, propertyDescriptor, value);     }   } } 

And in Application_Start put this:

ModelBinders.Binders.DefaultBinder = new EmptyStringToNullModelBinder();