Returns json result and convert null to empty string

Question

I have an action that returns json result, but some of the attributes are null and I want to convert them to empty strings instead. I heard I can use DefaultValue("") , but it's still returning null instead of empty string.

The action is:

[HttpGet]
public ActionResult GetResults(string date)
{
    var data= GetData();  // returns List<Foo>
    var json = Json(data, JsonRequestBehavior.AllowGet);
    return json;
}

The Foo class is:

public class Foo
{
    public string Bar1;

    [DefaultValue("")]
    public int? Bar2;
}

Answer 1

you can't set a nullable int to default val of ""

Try

[DefaultValue(0)]
public int? Bar2;

Answer 2

Like @Dave A noticed you can not assign string value to the int value.

However one thing that I wanted to warn it, have you set properly the property DefaultValueHandling ? Check it here: Removing Default Values in JSON with the MVC4 Web API

Besides that I would recommend to you that you do a string property that represent this Bar2 int property and you "Ignore" it for serialization, like:

[JsonIgnore]
[DefaultValue(0)]
public int? Bar2Int;

public string Bar2
{
   return { Bar2Int.HasValue ? this.Bar2Int.Value.ToString() : String.Empty; }
}

Even better with this approach you do not need any default values attributes.