ASP.NET MVC Int Array parameter with empty array defaults to {0}

Question

I have a controller action like:

Public ActionResult MyAction(int[] stuff){}

I make a JSON request like:

$.getJSON(url, { stuff: [] })

When it gets to C# it looks like an array with one element in it, which is zero (i.e. like if I did int[] stuff = {0};).

Is this new with MVC 2 or .NET 4? It seems to have changed recently, but I haven't found a smoking gun. How can I get around this? This can't possibly be expected behavior, can it?

Answer 1

I think this is a bug in MVC:

// create a vpr with raw value and attempted value of empty string
ValueProviderResult r = new ValueProviderResult("", "", System.Globalization.CultureInfo.CurrentCulture);
// this next line returns {0}
r.ConvertTo(typeof(int[]));

If we look at ValueProviderResult.cs in function UnwrapPossibleArrayType, we see:

// case 2: destination type is array but source is single element, so wrap element in array + convert
object element = ConvertSimpleType(culture, value, destinationElementType);
IList converted = Array.CreateInstance(destinationElementType, 1);
converted[0] = element;
return converted;

It forces converted[0] to be element, and ConvertSimpleType casts "" to 0. So I'm closing this question, unless someone has more info.

EDIT: Also, this is not in revision 17270, so if you're making a list of things which change from MVC 1 to MVC 2, this is one of them.

Answer 2

When I tested the code I got null array in the controller action and not an array with one element.

In jquery 1.4 and later the way parameters are serialized during an AJAX request have changed and is no longer compatible with the default model binder. You could set the traditional parameter when performing the request:

$.getJSON(url, $.param({ stuff: [ 1, 2, 3 ] }, true));

or

$.ajax({
    url: url,
    type: 'GET',
    dataType: 'JSON',
    data: { stuff: [ 1, 2, 3 ] },
    traditional: true,
    success: function(res) { }
});