Return List<object> in Csv format as response WCF C#

Question

I would like to return the List of my class objects as a csv file from my WCF method. I tried implementing custom formatter using MediaTypeFormatter given here Custom formatter

But I am not able to implement this in WCF service method. Is there a way of implementing this in WCF ? Can i somehow set my custom formatter in ResponseFormat and will it work ? I am looking for solution that directly converts my list to csv. I have simple service method defined in service interface as :

    [OperationContract]
    [WebInvoke(Method = "GET", BodyStyle = WebMessageBodyStyle.Bare, UriTemplate = "GetDNCList")]
    List<DNC> GetDNCList();

This List should go to user as a csv file

Answer 1

The custom formatter (and the MediaTypeFormatter) are used in the ASP.NET Web API framework, not in WCF. In this framework, you need to use an IDispatchMessageFormatter to control how the response is formatter. The post at http://blogs.msdn.com/b/carlosfigueira/archive/2011/05/03/wcf-extensibility-message-formatters.aspx has detailed information on how to implement this, and the code below shows one way of implementing a CSV formatter for WCF.

public class StackOverflow_23979866
{
    public class DNC
    {
        public string Field1 { get; set; }
        public string Field2 { get; set; }
        public string Field3 { get; set; }
    }
    [ServiceContract]
    public interface ITest
    {
        [OperationContract]
        [WebInvoke(Method = "GET", BodyStyle = WebMessageBodyStyle.Bare, UriTemplate = "GetDNCList")]
        List<DNC> GetDNCList();
    }
    public class Service : ITest
    {
        public List<DNC> GetDNCList()
        {
            return new List<DNC>
            {
                new DNC { Field1 = "Value 1-1", Field2 = "Value 2-1", Field3 = "Value 3-1" },
                new DNC { Field1 = "Value 1-2", Field2 = "Value 2-2", Field3 = "Value 3-2" },
                new DNC { Field1 = "Value 1-3", Field2 = "Value 2-3", Field3 = "Value 3-3" },
            };
        }
    }
    public class MyWebHttpBehavior : WebHttpBehavior
    {
        protected override IDispatchMessageFormatter GetReplyDispatchFormatter(OperationDescription operationDescription, ServiceEndpoint endpoint)
        {
            if (operationDescription.Name == "GetDNCList")
            {
                return new MyListOfDNCReplyFormatter();
            }
            else
            {
                return base.GetReplyDispatchFormatter(operationDescription, endpoint);
            }
        }
    }
    public class MyListOfDNCReplyFormatter : IDispatchMessageFormatter
    {
        public void DeserializeRequest(Message message, object[] parameters)
        {
            throw new NotSupportedException("This is a reply-only formatter");
        }

        public Message SerializeReply(MessageVersion messageVersion, object[] parameters, object result)
        {
            List<DNC> list = (List<DNC>)result;
            StringBuilder sb = new StringBuilder();
            sb.AppendLine("\"Field1\",\"Field2\",\"Field3\"");
            foreach (var dnc in list)
            {
                // may need to escape, leaving out for brevity
                sb.AppendLine(string.Format("\"{0}\",\"{1}\",\"{2}\"", dnc.Field1, dnc.Field2, dnc.Field3));
            }

            Message reply = Message.CreateMessage(messageVersion, null, new RawBodyWriter(sb.ToString()));
            reply.Properties.Add(WebBodyFormatMessageProperty.Name, new WebBodyFormatMessageProperty(WebContentFormat.Raw));
            HttpResponseMessageProperty httpResp = new HttpResponseMessageProperty();
            reply.Properties.Add(HttpResponseMessageProperty.Name, httpResp);
            httpResp.Headers[HttpResponseHeader.ContentType] = "text/csv";
            return reply;
        }

        class RawBodyWriter : BodyWriter
        {
            string contents;
            public RawBodyWriter(string contents)
                : base(true)
            {
                this.contents = contents;
            }

            protected override void OnWriteBodyContents(XmlDictionaryWriter writer)
            {
                writer.WriteStartElement("Binary");
                byte[] bytes = Encoding.UTF8.GetBytes(this.contents);
                writer.WriteBase64(bytes, 0, bytes.Length);
                writer.WriteEndElement();
            }
        }
    }
    public static void Test()
    {
        string baseAddress = "http://" + Environment.MachineName + ":8000/Service";
        ServiceHost host = new ServiceHost(typeof(Service), new Uri(baseAddress));
        ServiceEndpoint endpoint = host.AddServiceEndpoint(typeof(ITest), new WebHttpBinding(), "");
        endpoint.Behaviors.Add(new MyWebHttpBehavior());
        host.Open();
        Console.WriteLine("Host opened");

        WebClient c = new WebClient();
        Console.WriteLine(c.DownloadString(baseAddress + "/GetDNCList"));

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