Optional parameter in UriTemplate in WCF

问题:

I've used the hint in this thread and provided a default value, so that when a user doesnät specify the virutal sub-directory, I'm making the assumption that he meant all the stuff to be listed. It works.

[OperationContract]
[WebInvoke(UriTemplate = "GetStuff/{type=all}", ...]
IEnumerable<Stuff> GetStuff(String type);

However, it would be nicer to specify a default value, instead. However, default(String) is null and I'd like to sent in an actual value. Particularly, I've set my heart on String.Empty. However, I noticed that the following doesn't work. The condition on server side doesn't recognize the empty string (...where 'type' in (ColName, '', 'all')).

[OperationContract]
[WebInvoke(UriTemplate = "GetStuff/{type=String.Empty}", ...]
IEnumerable<Stuff> GetStuff(String type);

What to do?

回答1:

You can't really have an empty default value in an UriTemplate, but you can have something which will mean a default value, and at the operation you can replace that with the actual default value you want, as shown below.

public class StackOverflow_17251719
{
    const string DefaultValueMarker = "___DEFAULT_VALUE___";
    const string ActualDefaultValue = "";
    [ServiceContract]
    public class Service
    {
        [WebInvoke(UriTemplate = "GetStuff/{type=" + DefaultValueMarker + "}", ResponseFormat = WebMessageFormat.Json)]
        public IEnumerable<string> GetStuff(String type)
        {
            if (type == DefaultValueMarker)
            {
                type = ActualDefaultValue;
            }

            yield return type;
        }
    }
    public static void SendBodylessPostRequest(string uri)
    {
        HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(uri);
        req.Method = "POST";
        req.ContentType = "application/json";
        req.GetRequestStream().Close(); // no request body

        HttpWebResponse resp;
        try
        {
            resp = (HttpWebResponse)req.GetResponse();
        }
        catch (WebException e)
        {
            resp = (HttpWebResponse)e.Response;
        }

        Console.WriteLine("HTTP/{0} {1} {2}", resp.ProtocolVersion, (int)resp.StatusCode, resp.StatusDescription);
        foreach (string headerName in resp.Headers.AllKeys)
        {
            Console.WriteLine("{0}: {1}", headerName, resp.Headers[headerName]);
        }

        Console.WriteLine();
        Stream respStream = resp.GetResponseStream();
        Console.WriteLine(new StreamReader(respStream).ReadToEnd());

        Console.WriteLine();
        Console.WriteLine("  *-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*  ");
        Console.WriteLine();
    }
    public static void Test()
    {
        string baseAddress = "http://" + Environment.MachineName + ":8000/Service";
        WebServiceHost host = new WebServiceHost(typeof(Service), new Uri(baseAddress));
        host.Open();
        Console.WriteLine("Host opened");

        SendBodylessPostRequest(baseAddress + "/GetStuff/nonDefault");
        SendBodylessPostRequest(baseAddress + "/GetStuff");

        Console.Write("Press ENTER to close the host");
        Console.ReadLine();
        host.Close();
    }
}

回答2:

It worked with "=null" for me. My contract looks like this:

[WebInvoke(UriTemplate = "UploadFile/{fileName}/{patientId}/{documentId}/{providerName=null}", Method = "POST")]

void UploadFile(string fileName, string patientId, string documentId, string providerName, Stream fileContents);

回答3:

You do have the ability to add an optional parameter to your URITemplate. However, it has to be the last parameter.

Optional UriTemplate parameter using WebGet

回答4:

when adding only '=' to get a default value which is empty for string variable it throws the message

The UriTemplate '/applications/legal/statuses/{serviceId=}' is not valid; the UriTemplate variable declaration 'serviceId=' provides an empty default value to path variable 'serviceId'. Note that UriTemplate path variables cannot be bound to a null or empty value. See the documentation for UriTemplate for more details.

instead assign a default value and check later in the code:

 UriTemplate = "/applications/legal/statuses/{serviceId=default}"

service id will be default value.