【Expression 序列化】WCF的简单使用及其Expression Lambada的序列化问题初步解决方案（二）

接上文 【Expression 序列化】WCF的简单使用及其Expression Lambada的序列化问题初步解决方案（一） 

上文留下了一个问题没有处理，但最后也找到了相应的解决方案，下面就来说下问题的解决

Expression Tree Serializer 提供的解决方案是 把Expression表达式树转换为XElement类型的XML数据，传输到服务端，再反转换还原成原来的Expression表达式

所以，客户端与服务端之间传送的数据是XElement类型的数据了，从而避开了Expression类型不能序列化的问题

我们先来了解一下Expression Tree Serializer的使用，下载 Expression Tree Serializer 源代码进行编译，只需要用到其中的ExpressionSerialization.dll

新建一个控制台项目，添加ExpressionSerialization引用。先来试用一下ExpressionSerialization对Expression的处理

把Main方法修改为如下代码：

static void Main(string[] args)
{
    var sources = new[] { "abc", "abd", "bcd", "acd", "cdb" };
    Expression<Func<string, bool>> predicate = m => m.StartsWith("a");
    Console.WriteLine("使用原始Expression表达式查询数据：");
    Console.WriteLine(predicate);
    sources.Where(predicate.Compile()).ToList().ForEach(s => Console.Write(s + " "));
    Console.WriteLine();
    var serializer = new ExpressionSerializer();
    var xmlPredicate = serializer.Serialize(predicate);
    var newPredicate = serializer.Deserialize<Func<string, bool>>(xmlPredicate);
    Console.WriteLine("使用新Expression表达式查询数据：");
    Console.WriteLine(newPredicate);
    sources.Where(newPredicate.Compile()).ToList().ForEach(s => Console.Write(s + " "));
    Console.ReadLine();
}

注意：如提示无法生成请将控制台项目的“目标框架”由原来的“.NET Framework 4 Client Profie”修改为“.NET Framework 4”

运行控制台项目，得到如下结果，与预期一致：

有了成功的第一步，就敢大踏步往下走了，马上对上一文中的代码进行手术

对Services与Client项目分别添加ExpressionSerialization引用

WCF服务契约代码修改为如下：

[ServiceContract]
public interface IAccountContract
{
    [OperationContract]
    Member GetMember(XElement xmlPredicate);
}

WCF服务实现代码修改如下，为了在客户端显示服务端发生的异常信息，在服务实现类添加[ServiceBehavior(IncludeExceptionDetailInFaults = true)]特性：

[ServiceBehavior(IncludeExceptionDetailInFaults = true)]
public class AccountService : IAccountContract
{
    private readonly static List<Member> DataSource = new List<Member>
    {
        new Member {MemberID = 3, UserName = "zhangsan", Email = "zhangsan@abc.com"},
        new Member {MemberID = 4, UserName = "lisi", Email = "lisi@abc.com"},
        new Member {MemberID = 5, UserName = "wangwu", Email = "wangwu@abc.com"},
        new Member {MemberID = 6, UserName = "zhaoliu", Email = "zhaoliu@abc.com"}
    };

    public Member GetMember(XElement xmlPredicate)
    {
        var serializer = new ExpressionSerializer();
        var predicate = serializer.Deserialize<Func<Member, bool>>(xmlPredicate);
        return DataSource.SingleOrDefault(predicate.Compile());
    }
}

客户端代码修改如下：

static void Main(string[] args)
{
    Console.WriteLine("按任意建执行客户端调用：");
    Console.ReadLine();
    try
    {
        Expression<Func<Member, bool>> predicate = m => m.UserName == "zhangsan";
        var serializer = new ExpressionSerializer();
        var xmlPredicate = serializer.Serialize(predicate);
        var result = WcfHelper.InvokeService<IAccountContract, Member>(wcf => wcf.GetMember(xmlPredicate));
        Console.WriteLine(result.Email);
    }
    catch (Exception e)
    {
        Console.WriteLine(e);
    }
    Console.ReadLine();
}

再次注意：如提示无法生成请将控制台项目的“目标框架”由原来的“.NET Framework 4 Client Profie”修改为“.NET Framework 4”

我们再次信心满满的修改多项目启动，运行……服务端与客户端都如愿正常启动了：

 

但是，客户端按任意键执行调用的时候……客户端发生了如下异常：

捕捉到 System.ServiceModel.FaultException<System.ServiceModel.ExceptionDetail>
  Message=Could not find a matching type
参数名: Liuliu.Wcf.IContract.Member
  Source=mscorlib
  Action=http://schemas.microsoft.com/net/2005/12/windowscommunicationfoundation/dispatcher/fault
  StackTrace:
    Server stack trace: 
       在 System.ServiceModel.Channels.ServiceChannel.ThrowIfFaultUnderstood(Message reply, MessageFault fault, String action, MessageVersion version, FaultConverter faultConverter)
       在 System.ServiceModel.Channels.ServiceChannel.HandleReply(ProxyOperationRuntime operation, ProxyRpc& rpc)
       在 System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs, TimeSpan timeout)
       在 System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs)
       在 System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage methodCall, ProxyOperationRuntime operation)
       在 System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage message)
    Exception rethrown at [0]: 
       在 System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg)
       在 System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type)
       在 Liuliu.Wcf.IContract.IAccountContract.GetMember(XElement xmlPredicate)
       在 Liuliu.Wcf.Client.Program.<>c__DisplayClass1.<Main>b__0(IAccountContract wcf) 位置 D:\我的文档\Visual Studio 2010\Projects\LambadaSerializeDemo\Liuliu.Wcf.Client\Program.cs:行号 25
       在 Liuliu.Wcf.IContract.Helper.WcfHelper.InvokeService[TContract,TReturn](Func`2 func) 位置 D:\我的文档\Visual Studio 2010\Projects\LambadaSerializeDemo\Liuliu.Wcf.IContract\Helper\WcfHelper.cs:行号 30
       在 Liuliu.Wcf.Client.Program.Main(String[] args) 位置 D:\我的文档\Visual Studio 2010\Projects\LambadaSerializeDemo\Liuliu.Wcf.Client\Program.cs:行号 25
  InnerException: 

Liuliu.Wcf.IContract.Member类无法识别？！从客户端传过去的是数据是XElement的XML数据，因而ExpressionSerializer在进行反序列化操作的时候不知道有Liuliu.Wcf.IContract.Member这个类，知道大概也是只知其名而已
那就手动让ExpressionSerializer去详细了解Liuliu.Wcf.IContract.Member吧，万般查找发现了KnownTypeExpressionXmlConverter这个类，看名就知道，就是干这个使的。
修改服务实现代码如下：

public Member GetMember(XElement xmlPredicate)
{
    var assemblies = new List<Assembly> {typeof(Member).Assembly, typeof(ExpressionType).Assembly, typeof(IQueryable).Assembly};
    var resolver = new TypeResolver(assemblies, new[] {typeof(Member)});
    var knownTypeConverter = new KnownTypeExpressionXmlConverter(resolver);
    var serializer = new ExpressionSerializer(resolver, new CustomExpressionXmlConverter[] { knownTypeConverter });
    var predicate = serializer.Deserialize<Func<Member, bool>>(xmlPredicate);
    return DataSource.SingleOrDefault(predicate.Compile());
}

 客户端代码修改如下：

static void Main(string[] args)
{
    Console.WriteLine("按任意建执行客户端调用：");
    Console.ReadLine();
    try
    {
        Expression<Func<Member, bool>> predicate = m => m.UserName == "zhangsan";
        var assemblies = new List<Assembly> { typeof(Member).Assembly, typeof(ExpressionType).Assembly, typeof(IQueryable).Assembly };
        var resolver = new TypeResolver(assemblies, new[] { typeof(Member) });
        var knownTypeConverter = new KnownTypeExpressionXmlConverter(resolver);
        var serializer = new ExpressionSerializer(resolver, new CustomExpressionXmlConverter[] { knownTypeConverter });
        var xmlPredicate = serializer.Serialize(predicate);
        var result = WcfHelper.InvokeService<IAccountContract, Member>(wcf => wcf.GetMember(xmlPredicate));
        Console.WriteLine(result.Email);
    }
    catch (Exception e)
    {
        Console.WriteLine(e);
    }
    Console.ReadLine();
}

再次运行，报如下异常：

捕捉到 System.ServiceModel.FaultException<System.ServiceModel.ExceptionDetail>
  Message=序列不包含任何元素
  Source=mscorlib
  Action=http://schemas.microsoft.com/net/2005/12/windowscommunicationfoundation/dispatcher/fault
  StackTrace:
    Server stack trace: 
       在 System.ServiceModel.Channels.ServiceChannel.ThrowIfFaultUnderstood(Message reply, MessageFault fault, String action, MessageVersion version, FaultConverter faultConverter)
       在 System.ServiceModel.Channels.ServiceChannel.HandleReply(ProxyOperationRuntime operation, ProxyRpc& rpc)
       在 System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs, TimeSpan timeout)
       在 System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs)
       在 System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage methodCall, ProxyOperationRuntime operation)
       在 System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage message)
    Exception rethrown at [0]: 
       在 System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg)
       在 System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type)
       在 Liuliu.Wcf.IContract.IAccountContract.GetMember(XElement xmlPredicate)
       在 Liuliu.Wcf.Client.Program.<>c__DisplayClass2.<Main>b__1(IAccountContract wcf) 位置 D:\我的文档\Visual Studio 2010\Projects\LambadaSerializeDemo\Liuliu.Wcf.Client\Program.cs:行号 29
       在 Liuliu.Wcf.IContract.Helper.WcfHelper.InvokeService[TContract,TReturn](Func`2 func) 位置 D:\我的文档\Visual Studio 2010\Projects\LambadaSerializeDemo\Liuliu.Wcf.IContract\Helper\WcfHelper.cs:行号 30
       在 Liuliu.Wcf.Client.Program.Main(String[] args) 位置 D:\我的文档\Visual Studio 2010\Projects\LambadaSerializeDemo\Liuliu.Wcf.Client\Program.cs:行号 29
  InnerException: 

又查找了半天，没发现原因，想想会不会是数据的发送与接收不一致了，加了个在客户端发送前与服务端接收后都把相应的XElement数据写入文本文件中，一对比，居然真的不一样，吭爹啊……

 2.12KB VS 2.23KB

<LambdaExpression NodeType="Lambda" Name="" TailCall="false" CanReduce="false">
  <Type>
    <Type Name="System.Func`2">
      <Type Name="Liuliu.Wcf.IContract.Member" />
      <Type Name="System.Boolean" />
    </Type>
  </Type>
  <Parameters>
    <ParameterExpression NodeType="Parameter" Name="m" IsByRef="false" CanReduce="false">
      <Type>
        <Type Name="Liuliu.Wcf.IContract.Member" />
      </Type>
    </ParameterExpression>
  </Parameters>
  <Body>
    <BinaryExpression CanReduce="false" IsLifted="false" IsLiftedToNull="false" NodeType="Equal">
      <Right>
        <ConstantExpression NodeType="Constant" CanReduce="false">
          <Type>
            <Type Name="System.String" />
          </Type>
          <Value>zhangsan</Value>
        </ConstantExpression>
      </Right>
      <Left>
        <MemberExpression NodeType="MemberAccess" CanReduce="false">
          <Member MemberType="Property" PropertyName="UserName">
            <DeclaringType>
              <Type Name="Liuliu.Wcf.IContract.Member" />
            </DeclaringType>
            <IndexParameters />
          </Member>
          <Expression>
            <ParameterExpression NodeType="Parameter" Name="m" IsByRef="false" CanReduce="false">
              <Type>
                <Type Name="Liuliu.Wcf.IContract.Member" />
              </Type>
            </ParameterExpression>
          </Expression>
          <Type>
            <Type Name="System.String" />
          </Type>
        </MemberExpression>
      </Left>
      <Method MemberType="Method" MethodName="op_Equality">
        <DeclaringType>
          <Type Name="System.String" />
        </DeclaringType>
        <Parameters>
          <Type>
            <Type Name="System.String" />
          </Type>
          <Type>
            <Type Name="System.String" />
          </Type>
        </Parameters>
        <GenericArgTypes />
      </Method>
      <Conversion />
      <Type>
        <Type Name="System.Boolean" />
      </Type>
    </BinaryExpression>
  </Body>
  <ReturnType>
    <Type Name="System.Boolean" />
  </ReturnType>
</LambdaExpression>

<LambdaExpression NodeType="Lambda" Name="" TailCall="false" CanReduce="false" xmlns="">
  <Type>
    <Type Name="System.Func`2">
      <Type Name="Liuliu.Wcf.IContract.Member"></Type>
      <Type Name="System.Boolean"></Type>
    </Type>
  </Type>
  <Parameters>
    <ParameterExpression NodeType="Parameter" Name="m" IsByRef="false" CanReduce="false">
      <Type>
        <Type Name="Liuliu.Wcf.IContract.Member"></Type>
      </Type>
    </ParameterExpression>
  </Parameters>
  <Body>
    <BinaryExpression CanReduce="false" IsLifted="false" IsLiftedToNull="false" NodeType="Equal">
      <Right>
        <ConstantExpression NodeType="Constant" CanReduce="false">
          <Type>
            <Type Name="System.String"></Type>
          </Type>
          <Value>zhangsan</Value>
        </ConstantExpression>
      </Right>
      <Left>
        <MemberExpression NodeType="MemberAccess" CanReduce="false">
          <Member MemberType="Property" PropertyName="UserName">
            <DeclaringType>
              <Type Name="Liuliu.Wcf.IContract.Member"></Type>
            </DeclaringType>
            <IndexParameters></IndexParameters>
          </Member>
          <Expression>
            <ParameterExpression NodeType="Parameter" Name="m" IsByRef="false" CanReduce="false">
              <Type>
                <Type Name="Liuliu.Wcf.IContract.Member"></Type>
              </Type>
            </ParameterExpression>
          </Expression>
          <Type>
            <Type Name="System.String"></Type>
          </Type>
        </MemberExpression>
      </Left>
      <Method MemberType="Method" MethodName="op_Equality">
        <DeclaringType>
          <Type Name="System.String"></Type>
        </DeclaringType>
        <Parameters>
          <Type>
            <Type Name="System.String"></Type>
          </Type>
          <Type>
            <Type Name="System.String"></Type>
          </Type>
        </Parameters>
        <GenericArgTypes></GenericArgTypes>
      </Method>
      <Conversion></Conversion>
      <Type>
        <Type Name="System.Boolean"></Type>
      </Type>
    </BinaryExpression>
  </Body>
  <ReturnType>
    <Type Name="System.Boolean"></Type>
  </ReturnType>
</LambdaExpression>

对比以上数据可发现，

所有的空标签发送时表示为<empty />的形式，而在接收后表示为<empty></empty>的形式，而ExpressionSerialization并没有对这种情况进行处理

找到的问题所在，就能把问题解决掉

将ExpressionSerialization工程的ExpressionSerializer(Deserialize).cs 文件中的“if (xml.IsEmpty)”语句替换为“if (xml.IsEmpty || !xml.Elements().Any())”，共有3处，然后重新编译ExpressionSerialization，添加引用

再次运行程序，终于得到期待已久的结果了：

现在可以高歌：红军不怕远征难，万水千山只等闲……

目前为此基本上解决了Expression序列化的问题了，可是……某日突然报了这么个异常：

捕捉到 System.ServiceModel.FaultException<System.ServiceModel.ExceptionDetail>
  Message=值不能为 null。
参数名: typeName
  Source=mscorlib
  Action=http://schemas.microsoft.com/net/2005/12/windowscommunicationfoundation/dispatcher/fault
  StackTrace:
    Server stack trace: 
       在 System.ServiceModel.Channels.ServiceChannel.ThrowIfFaultUnderstood(Message reply, MessageFault fault, String action, MessageVersion version, FaultConverter faultConverter)
       在 System.ServiceModel.Channels.ServiceChannel.HandleReply(ProxyOperationRuntime operation, ProxyRpc& rpc)
       在 System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs, TimeSpan timeout)
       在 System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs)
       在 System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage methodCall, ProxyOperationRuntime operation)
       在 System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage message)
    Exception rethrown at [0]: 
       在 System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg)
       在 System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type)
       在 Liuliu.Wcf.IContract.IAccountContract.GetMember(XElement xmlPredicate)
       在 Liuliu.Wcf.Client.Program.<>c__DisplayClass4.<Main>b__2(IAccountContract wcf) 位置 D:\我的文档\Visual Studio 2010\Projects\LambadaSerializeDemo\Liuliu.Wcf.Client\Program.cs:行号 37
       在 Liuliu.Wcf.IContract.Helper.WcfHelper.InvokeService[TContract,TReturn](Func`2 func) 位置 D:\我的文档\Visual Studio 2010\Projects\LambadaSerializeDemo\Liuliu.Wcf.IContract\Helper\WcfHelper.cs:行号 30
       在 Liuliu.Wcf.Client.Program.Main(String[] args) 位置 D:\我的文档\Visual Studio 2010\Projects\LambadaSerializeDemo\Liuliu.Wcf.Client\Program.cs:行号 37
  InnerException: 

而发生异常的场景是这样的，在客户端代码添加了一个输入字符串作为查询条件的一部分（17行）：

客户端代码：

static void Main(string[] args)
{
    Console.WriteLine("按任意建执行客户端调用：");
    Console.ReadLine();
    try
    {
        Expression<Func<Member, bool>> predicate = m => m.UserName == "zhangsan";
        Console.WriteLine(predicate);
        var assemblies = new List<Assembly> { typeof(Member).Assembly, typeof(ExpressionType).Assembly, typeof(IQueryable).Assembly };
        var resolver = new TypeResolver(assemblies, new[] { typeof(Member) });
        var knownTypeConverter = new KnownTypeExpressionXmlConverter(resolver);
        var serializer = new ExpressionSerializer(resolver, new CustomExpressionXmlConverter[] { knownTypeConverter });
        var xmlPredicate = serializer.Serialize(predicate);
        var result = WcfHelper.InvokeService<IAccountContract, Member>(wcf => wcf.GetMember(xmlPredicate));
        Console.WriteLine(result.Email);

        var input = Console.ReadLine();
        if (!string.IsNullOrEmpty(input))
        {
            predicate = m => m.UserName == input;
            Console.WriteLine(predicate);
            xmlPredicate = serializer.Serialize(predicate);
            result = WcfHelper.InvokeService<IAccountContract, Member>(wcf => wcf.GetMember(xmlPredicate));
            Console.WriteLine(result.Email);
        }
    }
    catch (Exception e)
    {
        Console.WriteLine(e);
    }
    Console.ReadLine();
}

这样一个很正常的需求，居然又引出了一个大问题，详情请听下回分解^_^

 本文源代码下载：LambadaSerializeDemo02.rar