Question

I think I’ve found a bug in ASP.NET MVC controller’s parameters population

public JsonResult Lookup(
    string q_word, string primary_key, 
    int per_page, int page_num)

If the q_word posted value is empty string, q_word will receive an empty string. Whereas if you pack those parameters together (DRY principle) in an object, the behavior is different, empty string becomes null.

public class LookupArg
{
    public string q_word { get; set; }

    public string primary_key { get; set; }
    public int per_page { get; set; }
    public int page_num { get; set; }

    public string another_word { get; set; }
}


public JsonResult TesterA(
        string q_word, string another_word, string primary_key, 
        int per_page, int page_num)
{
    return Json(
                new { q_word, primary_key, per_page, page_num, another_word},
                JsonRequestBehavior.AllowGet);
}

public JsonResult TesterB(LookupArg la)
{
    return Json(
                new { la.q_word, la.primary_key, la.per_page, la.page_num, 
                      la.another_word }, 
                JsonRequestBehavior.AllowGet);
}

http://localhost:19829/Product/TesterA?q_word=&primary_key=id&per_page=10&page_num=1&another_word=
Has this output:

{"q_word":"","primary_key":"id","per_page":10,"page_num":1,"another_word":""}

http://localhost:19829/Product/TesterB?q_word=&primary_key=id&per_page=10&page_num=1&another_word=
Has this output:

{"q_word":null,"primary_key":"id","per_page":10,"page_num":1,"another_word":null}

I tried this too, but to no avail, same output, q_word and another_word are still nulls

public JsonResult TesterB(
   [Bind(Include = "q_word, primary_key, per_page, page_num, another_word")] 
   LookupArg la)

Is this sort of behavior expected? by design? should there be any difference if a value came from object or not?

Answer 1

You could decorate the property with the [DisplayFormat] attribute if you want to override this behavior which is by design since ASP.NET MVC 2 (it wasn’t the case in ASP.NET MVC 1, you may checkout the following blog post):

public class LookupArg
{
    [DisplayFormat(ConvertEmptyStringToNull = false)]
    public string q_word { get; set; }

    ...
}