ASP.Net MVC 3 bind string property as string.Empty instead of null

Question

model is

public partial class BilingualString 
{ 
    public string RuString { get; set; } 
    public string EnString { get; set; } 
} 

public partial class Member 
{  
   public Member() 
   { 
       this.DisplayName = new BilingualString(); 
   } 
   public BilingualString DisplayName { get; set; } 
}

if user don't fill inputs the values of RuString and EnString is null. I need string.Empty instead of null.

Using CustomModelBinder like this:

public class EmptyStringModelBinder : DefaultModelBinder 
{ 
    public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) 
    { 
        bindingContext.ModelMetadata.ConvertEmptyStringToNull = false; 
        return base.BindModel(controllerContext, bindingContext); 
    } 
}

don't help.

amiry jd · Accepted Answer · 2011-09-21 03:32:44Z

15

Use this:

    [DisplayFormat(ConvertEmptyStringToNull=false)]
    public string RuString { get; set; }

OR

    private string _RuString;
    public string RuString {
        get {
            return this._RuString ?? "";
        }
        set {
            this._RuString = value ?? "";
        }
    }

answered Sep 21, 2011 at 3:32

amiry jd

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4 Comments

AlexBBB Over a year ago

What if we don't want to mark every string field as [DisplayFormat(ConvertEmptyStringToNull=false)] ?

AlexBBB Over a year ago

The question is how to tell MVC 3 bind empty html input as string.Empty, not as null (like in MVC 1). The BilingualString is example to show that custom EmptyStringModelBinder don't do the do the trick.

amiry jd Over a year ago

I know what are you talking about. But I don't know any other way ): so sorry. If you find, put it here please. I'm following your Q. I think u have to use one of these 3 ways.

Manfred Over a year ago

I didn't want to write this on each string property so went with @Mike's answer.

Mike · Accepted Answer · 2014-08-25 04:44:19Z

2

old question, but here's an answer anyway :)

The issue seems to be that the ConvertEmptyStringToNull is set on the model binding context, not the property binding context.

Inside the DefaultModelBinder, it calls BindProperty for each property of the model, and doesn't recurse simple objects like strings/decimals down to their own call of BindModel.

Luckily we can override the GetPropertyValue instead and set the option on the context there.

public class EmptyStringModelBinder : DefaultModelBinder
{
   protected override object GetPropertyValue(ControllerContext controllerContext, ModelBindingContext bindingContext, System.ComponentModel.PropertyDescriptor propertyDescriptor, IModelBinder propertyBinder)
   {
       bindingContext.ModelMetadata.ConvertEmptyStringToNull = false;
       return base.GetPropertyValue(controllerContext, bindingContext, propertyDescriptor, propertyBinder);
   }
}

Worked for me :)

[edit] As pointed out in comments.. This model binder will only work if registered, so after adding class, be sure to call

ModelBinders.Binders.Add(typeof(string), new EmptyStringModelBinder());

in the Application_Start() method of Global.asax.cs

edited Aug 25, 2014 at 4:44

answered Jul 31, 2014 at 23:53

Mike

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2 Comments

Manfred Over a year ago

To make this work you also need to add ModelBinders.Binders.Add(typeof(string), new EmptyStringModelBinder()); in Application_Start(). After I added this line, it worked for me as well.

Mike Over a year ago

Sorry, my bad, I answered the OP's question on the assumption that they knew to do this given they'd already attempted a custom binder. didn't think about anyone else!

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