wcf - WCF 中 UriTemplate 中的可选参数

Question

我已经使用了 this thread 中的提示并提供了一个默认值，以便当用户没有指定虚拟子目录时，我假设他的意思是要列出所有内容。它有效。

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

但是，最好指定一个默认值。但是， default(String) 为空，我想发送一个实际值。特别是，我对 String.Empty 一心一意。但是，我注意到以下内容不起作用。服务器端的条件无法识别空字符串(... where 'type' in (ColName, '', 'all'))。

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

怎么办？

Answer 1

您不能在 UriTemplate 中真正拥有一个空的默认值，但是您可以拥有一些意味着默认值的东西，并且在操作中您可以将其替换为您想要的实际默认值，如下所示。

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();
    }
}