【Expression 序列化】WCF的簡單使用及其Expression Lambada的序列化問題初步解決方案（一）

在園子里混跡多年，始終保持着“只看帖不回帖”的習慣，看了很多，學了很多，卻從不敢寫些東西貼出來，一來沒什么可寫的，二來水平不夠，怕誤人子弟……

最近在做一個MVC+WCF+EF的項目，遇到問題不少，但大多數問題都是前人遇到並解決了的，感謝園子里的大牛們的無私奉獻。

俗話說“禮尚往來”，我也在此分享一個最近在項目中遇到的問題，就是遠程調用時的Expression表達式的序列化問題的初始解決方案，希望拋出的這塊石頭能引出完美的鑽石來，同時第一次寫博客，請大家多多賜教……

為了說明問題，我將用一個簡單的示例來演示，文章的最后會有示例的源代碼下載。

• 示例說明：

演示項目還是使用傳統的四層結構：

WCF服務契約：契約很簡單，一個Member類的Model，一個通過表達式來查找Member信息的GetMember(Expression<Func<Member, bool>>)方法

using System;
using System.Linq.Expressions;
using System.Runtime.Serialization;
using System.ServiceModel;

namespace Liuliu.Wcf.IContract
{
    [ServiceContract]
    public interface IAccountContract
    {
        [OperationContract]
        Member GetMember(Expression<Func<Member, bool>> predicate);
    }

    [DataContract]
    public class Member
    {
        [DataMember]
        public int MemberID { get; set; }

        [DataMember]
        public string UserName { get; set; }

        [DataMember]
        public string Email { get; set; }
    }
}

為簡化客戶端的調用操作，在Contracts項目中添加一個WcfHelper輔助類

using System;
using System.Collections.Generic;
using System.Linq;
using System.ServiceModel;
using System.Text;

namespace Liuliu.Wcf.IContract.Helper
{
    public class WcfHelper
    {
        public static TReturn InvokeService<TContract, TReturn>(Func<TContract, TReturn> func)
        {
            var channelFactory = new ChannelFactory<TContract>("*");
            var proxy = channelFactory.CreateChannel();
            var iproxy = proxy as ICommunicationObject;
            if (iproxy == null)
            {
                throw new ArgumentException("執行遠程方法時服務契約代理協議為空。");
            }
            try
            {
                iproxy.Open();
                var result = func(proxy);
                iproxy.Close();
                return result;
            }
            catch (CommunicationException)
            {
                iproxy.Abort();
                throw;
            }
            catch (TimeoutException)
            {
                iproxy.Abort();
                throw;
            }
            catch (Exception)
            {
                iproxy.Close();
                throw;
            }
        }
    }
}

服務的實現也非常簡單，就是從數據源DataSource中按條件查找相關信息並返回

using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using Liuliu.Wcf.IContract;

namespace Liuliu.Wcf.Services
{
    public class AccountService : IAccountContract
    {
        private readonly static List<Member> DataSource = new List<Member>
        {
            new Member {MemberID = 3, UserName = "zhangsan", Email = "[e-mail]"},
            new Member {MemberID = 4, UserName = "lisi", Email = "[e-mail]"},
            new Member {MemberID = 5, UserName = "wangwu", Email = "[e-mail]"},
            new Member {MemberID = 6, UserName = "zhaoliu", Email = "[e-mail]"}
        };

        public Member GetMember(Expression<Func<Member, bool>> predicate)
        {
            return DataSource.SingleOrDefault(predicate.Compile());
        }
    }
}

服務端以一個控制台的程序來承載，第一次寫博客，可以力求完美一點^_^

using System;
using System.Collections.Generic;
using System.Linq;
using System.ServiceModel;

using Liuliu.Wcf.Services;

namespace Liuliu.Wcf.Hosting
{
    class Program
    {
        private static readonly List<ServiceHost> OpenedHosts = new List<ServiceHost>();

        private static void Main(string[] args)
        {
            try
            {
                var accountHost = new ServiceHost(typeof(AccountService));
                var hosts = new List<ServiceHost> { accountHost };
                CreateHosting(hosts);
                OpenHosting(hosts);
                Console.WriteLine("按任意鍵關閉服務。");
                Console.ReadKey();
                CloseHosting(OpenedHosts);

            }
            catch (Exception e)
            {
                Console.WriteLine(e);
                Console.ReadLine();
            }
        }

        private static void OpenHosting(IEnumerable<ServiceHost> hosts)
        {
            foreach (var host in hosts)
            {
                try
                {
                    host.Open();
                    if (!OpenedHosts.Contains(host))
                    {
                        OpenedHosts.Add(host);
                    }
                }
                catch (Exception)
                {
                    foreach (var openedHost in OpenedHosts)
                    {
                        openedHost.Close();
                    }
                    throw;
                }
            }
        }

        private static void CreateHosting(IEnumerable<ServiceHost> hosts)
        {
            hosts.ToList().ForEach(host =>
            {
                host.Opened += host_Opened;
                host.Closed += host_Closed;
                host.UnknownMessageReceived += host_UnknownMessageReceived;
            });
        }

        private static void CloseHosting(IEnumerable<ServiceHost> hosts)
        {
            hosts.ToList().ForEach(host => host.Close());
        }

        static void host_UnknownMessageReceived(object sender, UnknownMessageReceivedEventArgs e)
        {
            var host = (ServiceHost)sender;
            Console.WriteLine("{0}收到未知消息。", host.Description.ConfigurationName);
        }

        static void host_Closed(object sender, EventArgs e)
        {
            var host = (ServiceHost)sender;
            Console.WriteLine("{0}已成功關閉。", host.Description.ConfigurationName);
        }

        static void host_Opened(object sender, EventArgs e)
        {
            var host = (ServiceHost)sender;
            Console.WriteLine("{0}服務啟動完畢\n監聽地址：{1}", host.Description.ConfigurationName, host.Description.Endpoints.First().ListenUri);
        }
    }
}

當然現在服務端還不能啟動，還需要必要的配置信息，在Hosting項目中添加一個App.Config來進行配置，可以通過VS2010中菜單“工具” - “WCF服務配置編輯器” 來進行可視化添加

為了簡化配置，這里不進行調用的驗證了，設置 clientCredentialType="None"

 

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <system.serviceModel>
        <bindings>
            <netTcpBinding>
                <binding name="NewBinding0">
                    <security>
                        <message clientCredentialType="None" />
                    </security>
                </binding>
            </netTcpBinding>
        </bindings>
        <services>
            <service name="Liuliu.Wcf.Services.AccountService">
                <endpoint address="net.tcp://127.0.0.1:9000/account" binding="netTcpBinding"
                    bindingConfiguration="NewBinding0" contract="Liuliu.Wcf.IContract.IAccountContract" />
            </service>
        </services>
    </system.serviceModel>
</configuration>

 

 

 

有了前面的WcfHelper的輔助，客戶端調用就非常愜意了，由UserName查找Member信息並顯示結果的Email信息

using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Text;

using Liuliu.Wcf.IContract;
using Liuliu.Wcf.IContract.Helper;

namespace Liuliu.Wcf.Client
{
    class Program
    {
        static void Main(string[] args)
        {
            Expression<Func<Member, bool>> predicate = m => m.UserName == "張三";
            var result = WcfHelper.InvokeService<IAccountContract, Member>(wcf => wcf.GetMember(predicate));
            Console.WriteLine(result.Email);
        }
    }
}

當然，還要客戶端的配置信息，由“WCF服務配置編輯器”工具可直接由上面配置的服務端配置來生成客戶端配置

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <system.serviceModel>
        <bindings>
            <netTcpBinding>
                <binding name="NewBinding0">
                    <security>
                        <message clientCredentialType="None" />
                    </security>
                </binding>
            </netTcpBinding>
        </bindings>
        <client>
            <endpoint address="net.tcp://127.0.0.1:9000/account" binding="netTcpBinding"
                bindingConfiguration="NewBinding0" contract="Liuliu.Wcf.IContract.IAccountContract"
                name="" kind="" endpointConfiguration="" />
        </client>
    </system.serviceModel>
</configuration>

 

至此，演示項目的基本架構搭建完畢，理論上運行的話應該能順利啟動，右鍵解決方案 - 設置啟動項目，設置啟動為多項目啟動：

當我們信心滿滿的點下啟動按鍵之后，結果卻不是我們所期待的，服務端在執行到OpenHosting(hosts)的時候引發了異常：

捕捉到 System.Runtime.Serialization.InvalidDataContractException
  Message=無法序列化類型“System.Linq.Expressions.Expression`1[System.Func`2[Liuliu.Wcf.IContract.Member,System.Boolean]]”。請考慮將其標以 DataContractAttribute 特性，並將其所有要序列化的成員標以 DataMemberAttribute 特性。如果類型為集合，則請考慮將其標以 CollectionDataContractAttribute 特性。有關其他受支持的類型，請參見 Microsoft .NET Framework 文檔。
  Source=System.Runtime.Serialization
  StackTrace:
       在 System.Runtime.Serialization.DataContract.DataContractCriticalHelper.ThrowInvalidDataContractException(String message, Type type)
       在 System.Runtime.Serialization.DataContract.DataContractCriticalHelper.CreateDataContract(Int32 id, RuntimeTypeHandle typeHandle, Type type)
       在 System.Runtime.Serialization.DataContract.DataContractCriticalHelper.GetDataContractSkipValidation(Int32 id, RuntimeTypeHandle typeHandle, Type type)
       在 System.Runtime.Serialization.XsdDataContractExporter.GetSchemaTypeName(Type type)
       在 System.ServiceModel.Dispatcher.DataContractSerializerOperationFormatter.ValidateDataContractType(Type type)
       在 System.ServiceModel.Dispatcher.DataContractSerializerOperationFormatter.CreatePartInfo(MessagePartDescription part, OperationFormatStyle style, DataContractSerializerOperationBehavior serializerFactory)
       在 System.ServiceModel.Dispatcher.DataContractSerializerOperationFormatter.CreateMessageInfo(DataContractFormatAttribute dataContractFormatAttribute, MessageDescription messageDescription, DataContractSerializerOperationBehavior serializerFactory)
       在 System.ServiceModel.Dispatcher.DataContractSerializerOperationFormatter..ctor(OperationDescription description, DataContractFormatAttribute dataContractFormatAttribute, DataContractSerializerOperationBehavior serializerFactory)
       在 System.ServiceModel.Description.DataContractSerializerOperationBehavior.GetFormatter(OperationDescription operation, Boolean& formatRequest, Boolean& formatReply, Boolean isProxy)
       在 System.ServiceModel.Description.DataContractSerializerOperationBehavior.System.ServiceModel.Description.IOperationBehavior.ApplyDispatchBehavior(OperationDescription description, DispatchOperation dispatch)
       在 System.ServiceModel.Description.DispatcherBuilder.BindOperations(ContractDescription contract, ClientRuntime proxy, DispatchRuntime dispatch)
       在 System.ServiceModel.Description.DispatcherBuilder.InitializeServiceHost(ServiceDescription description, ServiceHostBase serviceHost)
       在 System.ServiceModel.ServiceHostBase.InitializeRuntime()
       在 System.ServiceModel.ServiceHostBase.OnBeginOpen()
       在 System.ServiceModel.ServiceHostBase.OnOpen(TimeSpan timeout)
       在 System.ServiceModel.Channels.CommunicationObject.Open(TimeSpan timeout)
       在 System.ServiceModel.Channels.CommunicationObject.Open()
       在 Liuliu.Wcf.Hosting.Program.OpenHosting(IEnumerable`1 hosts) 位置 D:\我的文檔\Visual Studio 2010\Projects\LambadaSerializeDemo\Liuliu.Wcf.Hosting\Program.cs:行號 52
       在 Liuliu.Wcf.Hosting.Program.Main(String[] args) 位置 D:\我的文檔\Visual Studio 2010\Projects\LambadaSerializeDemo\Liuliu.Wcf.Hosting\Program.cs:行號 21
  InnerException: 

 

由異常信息我們可以很明確的看到，System.Linq.Expressions.Expression類不支持序列化操作，以Expression作為查詢條件的參數傳遞是行不通的。
此路不通，我們只能另辟蹊徑了

以“Expression”，“序列化”，“Lambada”等為關鍵字百度Google了一把，終於還是收獲不少，找到了Expression Tree Serializer 這根救命稻草

有路了就要往下走，后面還會遇到什么問題，且聽下回分解……

 最后，把本文的源代碼發上來以供參考，注意：為了保持現場，這個源碼包的程序並不能運行

LambadaSerializeDemo01.rar