Consuming REST Service with WCF - Optional Querystring Parameters?

Question

I am having problems trying to consume a simple service using WCF. Everything has gone well so far except when coming to implement optional query string parameters. The interface looks a bit like this:

[ServiceContract]
[XmlSerializerFormat]
public interface IApi
{
    [OperationContract]
    [WebGet(UriTemplate = "/url/{param}?top={top}&first={first}")]
    object GetStuff(string param, int top, DateTime first);
}

Then this is consumed by creating a class that inherits ClientBase<IApi>. I tried a few ways to make the parameters optional:

1) Make the parameters nullable

This did not work. I get a message from the QueryStringConverter like another question has asked: Can a WCF service contract have a nullable input parameter?

2) One Parameter at the end of the URL

So, I thought about changing the UriTemplate to be more generic, building the query string and passing it through as a parameter. This didn't seem to work either, as the value passed in gets encoded such that it is not recognised as a querystring by the server.

Example:

[WebGet(UriTemplate = "/url/{query}")]

3) Hackish Solution

The only way I found so far of getting this to work is to change all the parameters to strings, and NULL's seem to be allowed here.

Example:

[WebGet(UriTemplate = "/url/{param}?top={top}&first={first}")]
object GetStuff(string param, string top, string first);

The consumption of this interface still accepts the correct variable type, but ToString is used. Thes query string parameters still appear in the actual request.

So, is there a way when consuming a REST service using WCF, to make the query string parameters optional?

UPDATE - How it was fixed

The advice to create a service behaviour was taken. This inherits from WebHttpBehaviour. It looks as follows:

public class Api : ClientBase<IApi>
{
    public Api() : base("Binding")
    {
        Endpoint.Behaviors.Add(new NullableWebHttpBehavior());
    }
}

The NullableWebHttpBehavior can be found at the following Stackoverflow question: Can a WCF service contract have a nullable input parameter?. The only problem was, ConvertValueToString wasn't overloaded, so I whipped a quick one up:

    public override string ConvertValueToString(object parameter, Type parameterType)
    {
        var underlyingType = Nullable.GetUnderlyingType(parameterType);

        // Handle nullable types
        if (underlyingType != null)
        {
            var asString = parameter.ToString();

            if (string.IsNullOrEmpty(asString))
            {
                return null;
            }

            return base.ConvertValueToString(parameter, underlyingType);
        }

        return base.ConvertValueToString(parameter, parameterType);
    }

This may not be perfect, but it seems to work as intended.

Answer 1

Your option 1) can work for a WCF client because the WebHttpBehavior can be applied to a ClientBase (or ChannelFactory) derived class as shown in this SO question & answer. Just combine the code you reference in 1) with the configuration shown in the capturing 500 responses question and it show work.