WCF - 将空元素转换为可为空的 native 类型

Question

将 SOAP 字段元素留空会导致 native 类型的转换错误。 (遗憾的是，由于客户端限制，无法使用 xsi:nil="true")

将 WCF 契约(Contract) native 类型标记为 nullable<> 似乎不足以阻止将以下错误返回给客户端。

The string '' is not a valid Boolean value. at System.Xml.XmlConvert.ToBoolean(String s) at System.Xml.XmlConverter.ToBoolean(String value) System.FormatException

有谁知道指示 DataContractSerializer 将要反序列化的空元素转换为 null 的最佳方法？

我的示例 WCF 服务契约(Contract)；

[ServiceContract()]
public interface IMyTest
{
    [OperationContract]
    string TestOperation(TestRequest request);
}

[ServiceBehavior()]
public class Settings : IMyTest
{
    public string TestOperation(TestRequest request)
    {
        if (request.TestDetail.TestBool.HasValue)
            return "Bool was specified";
        else
            return "Bool was null";
    }

}

[DataContract()]
public class TestRequest
{
    [DataMember(IsRequired = true)]
    public int ID { get; set; }

    [DataMember(IsRequired = true)]
    public TestDetail TestDetail { get; set; }
}

[DataContract()]
public class TestDetail
{
    [DataMember()]
    public bool? TestBool { get; set; }
}

我们如何才能让 WCF 接受以下提交；

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ster="mynamespace">
   <soapenv:Header/>
   <soapenv:Body>
      <ster:TestOperation>
         <ster:request>
            <ster:ID>1</ster:ID>
            <ster:TestDetail>
               <ster:TestBool></ster:TestBool>
            </ster:TestDetail>
         </ster:request>
      </ster:TestOperation>
   </soapenv:Body>
</soapenv:Envelope>

客户端只能更改它插入的值 <ster:TestBool>{here}</ster:TestBool>所以 true false or nothing 是唯一的选择。

Answer 1

好的，我相信我已经通过使用操作行为来修改底层消息，然后再通过 IDispatchMessageFormatter 对其进行格式化。

以下代码针对基于 WCF 无文件激活的服务提供了解决方案。

我想让我的 IOperationBehavior 以 Attribute 类的形式存在。然后我可以简单地用我的新属性装饰每个服务操作，这将激发该操作的 IOperationBehavior - 对最终用户来说非常好和简单。

关键问题是你在哪里应用行为，这很关键。通过属性应用行为时，WCF 调用的操作行为的顺序与在服务主机应用时不同。基于属性的顺序如下:

System.ServiceModel.Dispatcher.OperationInvokerBehavior

我的操作行为属性

System.ServiceModel.OperationBehaviorAttribute

System.ServiceModel.Description.DataContractSerializerOperationBehavior

System.ServiceModel.Description.DataContractSerializerOperationGenerator

由于某种原因，操作行为(仅当通过使用属性应用时)将被称为 之前 DataContractSerializerOperationBehavior。这是一个问题，因为在我的行为中，在我调整了消息(参见代码)之后，我想将反序列化委托(delegate)给我的格式化程序中的 DataContractSerializerOperationBehavior 格式化程序(作为内部格式化程序传递给我的行为)。当微软已经提供了一个非常好的反序列化器时，我不想重新编写反序列化例程。我只是在第一个实例中更正 XML，以便将空白转换为在 XML 中正确表示的空值，以便 DataContractSerializer 可以将它们绑定(bind)到服务接口(interface)中的可为空类型。

因此，这意味着我们不能按预期使用基于属性的行为，因为 WCF 很可能在这里以一种相当微妙的方式被破坏，因为我看不出这种现象的原因。所以我们仍然可以在操作中添加一个 IOperationBehavior，我们只需要在服务主机创建阶段手动分配它，因为然后我们的 IOperationBehavior 被插入到“正确”的序列中，即在创建 DataContractSerializerOperationBehavior 之后，只有这样我可以引用内部格式化程序吗？

 // This operation behaviour changes the formatter for a specific set of operations in a web service.

[System.AttributeUsage(System.AttributeTargets.Method, AllowMultiple = false)]
public class NullifyEmptyElementsAttribute : Attribute
{
    // just a marker, does nothing
}

public class NullifyEmptyElementsBahavior : IOperationBehavior
{
    #region IOperationBehavior Members

    public void AddBindingParameters(OperationDescription operationDescription, System.ServiceModel.Channels.BindingParameterCollection bindingParameters) 
    {

    }

    public void ApplyClientBehavior(OperationDescription operationDescription, ClientOperation clientOperation) {  }

    public void ApplyDispatchBehavior(OperationDescription operationDescription, DispatchOperation dispatchOperation)
    {
        // we are the server, we need to accept client message that omit the xsi:nill on empty elements
        dispatchOperation.Formatter = new NullifyEmptyElementsFormatter(dispatchOperation.Formatter);

    }

    public void Validate(OperationDescription operationDescription) { }

    #endregion IOperationBehavior Members
}

/// <summary>
///  This customized formatter intercepts the deserialization process to perform extra processing.
/// </summary>
public class NullifyEmptyElementsFormatter : IDispatchMessageFormatter
{
    // Hold on to the original formatter so we can use it to return values for method calls we don't need.
    private IDispatchMessageFormatter _innerFormatter;

    public NullifyEmptyElementsFormatter(IDispatchMessageFormatter innerFormatter)
    {
        // Save the original formatter
        _innerFormatter = innerFormatter;
    }

    /// <summary>
    /// Check each node and add the xsi{namespace}:nil declaration if the inner text is blank
    /// </summary>
    public static void MakeNillable(XElement element)
    {
        XName _nillableAttributeName = "{http://www.w3.org/2001/XMLSchema-instance}nil"; // don't worry, the namespace is what matters, not the alias, it will work

        if (!element.HasElements) // only end nodes
        {
            var hasNillableAttribute = element.Attribute(_nillableAttributeName) != null;

            if (string.IsNullOrEmpty(element.Value))
            {
                if (!hasNillableAttribute)
                    element.Add(new XAttribute(_nillableAttributeName, true));
            }
            else
            {
                if (hasNillableAttribute)
                    element.Attribute(_nillableAttributeName).Remove();
            }
        }
    }

    public void DeserializeRequest(System.ServiceModel.Channels.Message message, object[] parameters)
    {


var buffer = message.CreateBufferedCopy(int.MaxValue);

        var messageSource = buffer.CreateMessage(); // don't affect the underlying stream

        XDocument doc = null;

        using (var messageReader = messageSource.GetReaderAtBodyContents())
        {
            doc = XDocument.Parse(messageReader.ReadOuterXml()); // few issues with encoding here (strange bytes at start of string), this technique resolves that
        }

        foreach (var element in doc.Descendants())
        {
            MakeNillable(element);
        }

        // create a new message with our corrected XML
        var messageTarget = Message.CreateMessage(messageSource.Version, null, doc.CreateReader());
        messageTarget.Headers.CopyHeadersFrom(messageSource.Headers);

        // now delegate the work to the inner formatter against our modified message, its the parameters were after
         _innerFormatter.DeserializeRequest(messageTarget, parameters);
    }

    public System.ServiceModel.Channels.Message SerializeReply(System.ServiceModel.Channels.MessageVersion messageVersion, object[] parameters, object result)
    {
        // Just delegate this to the inner formatter, we don't want to do anything with this.
        return _innerFormatter.SerializeReply(messageVersion, parameters, result);
    }
}


public class MyServiceHost : ServiceHost
{
    public MyServiceHost(Type serviceType, params Uri[] baseAddresses)
        : base(serviceType, baseAddresses) { }

     protected override void OnOpening()
    {
        base.OnOpening();

        foreach (var endpoint in this.Description.Endpoints)
        {
            foreach (var operation in endpoint.Contract.Operations)
            {
                if ((operation.BeginMethod != null && operation.BeginMethod.GetCustomAttributes(_NullifyEmptyElementsBahaviorAttributeType, false).Length > 0)
                       ||
                       (operation.SyncMethod != null && operation.SyncMethod.GetCustomAttributes(_NullifyEmptyElementsBahaviorAttributeType, false).Length > 0)
                       ||
                       (operation.EndMethod != null && operation.EndMethod.GetCustomAttributes(_NullifyEmptyElementsBahaviorAttributeType, false).Length > 0))
                {
                    operation.Behaviors.Add(new NullifyEmptyElementsBahavior());
                }
            }
        }
    }
}

也许因为我只是在修改传入的消息，我可以改用 IDispatchMessageInspector，这将消除对 IDispatchMessageFormatter 激活顺序的依赖。但这暂时有效；)

用法:

加入您的运营

 [ServiceContract(Namespace = Namespaces.MyNamespace)]
 public interface IMyServiceContrct
 {
       [OperationContract]
       [NullifyEmptyElements]
       void MyDoSomthingMethod(string someIneteger);
 }

为您服务

A. 如果您有 .svc，只需引用 MyServiceHost

<%@ ServiceHost 
    Language="C#" 
    Debug="true" 
    Service="MyNameSpace.MyService"
    Factory="MyNameSpace.MyServiceHost"  %>

B. 如果您使用无文件激活服务，请将其添加到您的 web.config 文件中

   <system.serviceModel>
        ... stuff
        <serviceHostingEnvironment multipleSiteBindingsEnabled="true" >

          <!-- WCF File-less service activation - there is no need to use .svc files anymore, WAS in IIS7 creates a host dynamically - less config needed-->
          <serviceActivations >  
            <!-- Full access to Internal services -->
            <add relativeAddress="MyService.svc" 
                 service="MyNameSpace.MyService" 
                 factory="MyNameSpace.MyServiceHost" />

          </serviceActivations>


        </serviceHostingEnvironment>
        ... stuff
    </system.serviceModel>