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POWCF REST Service: WebInvoke with JSON and polymorphism does not work correctly
 

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  1. POWCF REST Service: WebInvoke with JSON and polymorphism does not work correctly
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    <p>I have a typical WCF REST service in C# which accepts JSON input and returns a JSON output:</p> <pre><code>[ServiceContract] public class WCFService { [WebInvoke(Method = "POST", UriTemplate = "register", ResponseFormat = WebMessageFormat.Json)] public BasicResponse RegisterNewUser(UserDTO newUser) { return new BasicResponse() { status = "ERR_USER_NAME" }; } } public class BasicResponse { public string status { get; set; } } public class UserDTO { public string username { get; set; } public string authCode { get; set; } } </code></pre> <p>This works as expected but I want to return different objects in case of normal execution and in case of error. I created a base response class and few inheritors. Now the WCF JSON serializer crashes and produces "400 Bad Request":</p> <pre><code>[ServiceContract] public class WCFService { [WebInvoke(Method = "POST", UriTemplate = "register", ResponseFormat = WebMessageFormat.Json)] public BasicResponse RegisterNewUser(UserDTO newUser) { return new ErrorResponse() { status = "ERR_USER_NAME", errorMsg = "Invalid user name." }; } } public class BasicResponse { public string status { get; set; } } public class ErrorResponse : BasicResponse { public string errorMsg { get; set; } } public class UserDTO { public string username { get; set; } public string authCode { get; set; } } </code></pre> <p>I tried to apply the <code>[KnownType(typeof(ErrorResponse))]</code> and <code>[ServiceKnownType(typeof(ErrorResponse))]</code> attributes without any success. Seems like a bug in the <code>DataContractJsonSerializer</code> which states it supports polymorphism.</p> <p>My WCF REST service uses the WebServiceHostFactory:</p> <pre><code>&lt;%@ ServiceHost Language="C#" Debug="true" Service="WCFService" CodeBehind="CryptoCharService.svc.cs" Factory="System.ServiceModel.Activation.WebServiceHostFactory" %&gt; </code></pre> <p>In my Web.config I have standard HTTP endpoint:</p> <pre><code>&lt;system.serviceModel&gt; &lt;standardEndpoints&gt; &lt;webHttpEndpoint&gt; &lt;standardEndpoint helpEnabled="true" defaultOutgoingResponseFormat="Json" /&gt; &lt;/webHttpEndpoint&gt; &lt;/standardEndpoints&gt; &lt;/system.serviceModel&gt; </code></pre> <p>Do you think this is fixable? I know a workaround (to return string and serialize the output manually) but why this does not work?</p>
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