How to build web service/web api with optional parameters in C#

Question

I'm building a web API using web service. Users may use it like this: http://www.example.com/example.asmx/hello?param1=str&param2=str

or:

http://www.example.com/example.asmx/hello?param1=str .

I want to make param1 required while param2 optional.But my code below always throws an exception that says missing values for parameters when I try to call http://www.example.com/example.asmx/hello?param1=str. It works fine with http://www.example.com/example.asmx/hello?param1=str&param2=str.

[WebMethod]
public string hello(int param1, int param2 = 0)
{
 return "hello!";
}

Is there any way to fix it? If not, what techniques can I use to build a web API that accept optional parameters which is very common in public APIs. I'm a newbie so I don't know if web service is a good choice for building web APIs. Any help is appreciated.

• I4V: stackoverflow.com/questions/15852859/…
• ChandlerQ: @l4V Thanks! Seems I need to learn something about WCF. I'll give it a try and see if it works.
• Youssef Moussaoui: You may want to think about using ASP.NET Web API. I'm pretty sure it handles that case correctly and it's designed specifically for building Web APIs.
• ChandlerQ: @YoussefMoussaoui I'll google something about ASP.NET Web API, thanks for your help.
• ChandlerQ: @YoussefMoussaoui Thanks for your help! I've tried Web API and it works like a charm! That's exactly what I'm looking for.

Answer 1

basically you cant do that.

i suggest you to read this article first: http://blogs.msdn.com/b/jmstall/archive/2012/04/16/how-webapi-does-parameter-binding.aspx

it explains pretty well how parameters are bound.

• Youssef Moussaoui: I don't think he's using Web API at all.
• maxlego: regarding to sample uri's, then yes, i agree.

Answer 2

have you considered to use params which works within applications (wpf / winforms).

 // not tested
 [WebMethod]
 public string hello(params int[] list)
 {
 string s = "Hello\n";
 // do some stuff with your ints
 for ( int i = 0 ; i < list.Length ; i++ )
 s += list[i] + "\n" ;
 return s;
 }

• ChandlerQ: well,parameters here are name/value pair. Say, 1http://www.example.com/example.asmx/hello?userid=a1b2&count=5. Both the paremeter name and parameter value are needed. I suppose your method doesn't support name/value type parameters.

Answer 3

The problem probably is that for web method this parameter is required. Maybe this will help.

In accordance with MinOccurs Attribute Binding Support and Default Attribute Binding Support:

1. Value type accompanied by a public bool field that uses the Specified naming convention described previously under Translating XSD to source - minOccurs value of output <element> element 0.

   [WebMethod]
   public SomeResult SomeMethod(bool optionalParam, [XmlIgnore] bool optionalParamSpecified)

   result:

   <s:element minOccurs="0" maxOccurs="1" name="optionalParam" type="s:boolean" />

2. Value type with a default value specified via a System.Component.DefaultValueAttribute - minOccurs value of output <element> element 0. In the <element> element, the default value is also specified via the default XML attribute.

   [WebMethod]
   public SomeResult SomeMethod([DefaultValue(true)] bool optionalParam)

   result:

   <s:element minOccurs="0" maxOccurs="1" default="true" name="optionalParam" type="s:boolean" />