WCF中UriTemplate中的可选参数 [英] Optional parameter in UriTemplate in WCF

问题描述

我使用了此线程中的提示，并提供了默认值，因此，当用户未指定重要的子目录时，我假设他的意思是列出所有内容.可以.

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);

但是，最好指定一个默认值.但是， default(String)为 null ，我想发送一个实际值.特别是，我对 String.Empty 表示了放心.但是，我注意到以下操作无效.服务器端的条件无法识别空字符串( ...其中(ColName，''，'all')中的'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);

该怎么办?

推荐答案

在UriTemplate中，您不能真正拥有默认的空值，但是您可以拥有一些将意味着默认值的东西，并且在操作时您可以替换具有所需的实际默认值，如下所示.

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();
    }
}

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