Marking a referenced library class in WCF service

Question

This is in relation to a previous question I asked:

I have a DLL defining a Transaction class. It is referenced by a WCF service library as well as a client application. I get errors stating that the service library cannot be hosted because it can't serialise the DLL class.

Here's the service code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.Serialization;
using System.ServiceModel;
using System.Text;
using ServerLibrary.MarketService;
using SharedLibrary; // This is the DLL in question

namespace ServerLibrary
{
    [ServiceContract]
    public interface IService
    {
        [OperationContract]
        string GetData(int value);

        [OperationContract]
        CompositeType GetDataUsingDataContract(CompositeType composite);

        [OperationContract]
        bool ProcessTransaction(SharedLibrary.Transaction transaction);
    }

    [DataContract]
    public class CompositeType
    {
        bool boolValue = true;
        string stringValue = "Hello ";

        [DataMember]
        public bool BoolValue
        {
            get { return boolValue; }
            set { boolValue = value; }
        }

        [DataMember]
        public string StringValue
        {
            get { return stringValue; }
            set { stringValue = value; }
        }
    }
}

Do I have to mark the Transaction class here with [attribute] headers?

[UPDATE]

Here's the error messages I get when I try to host this service:

System.Runtime.Serialization.InvalidDataContractException: Type 'SharedLibrary.Transaction' cannot be serialized. Consider marking it with the DataContractAttribute attribute, and marking all of its members you want serialized with the DataMemberAttribute attribute. If the type is a collection, consider marking it with the CollectionDataContractAttribute. See the Microsoft .NET Framework documentation for other supported types. at System.Runtime.Serialization.DataContract.DataContractCriticalHelper.ThrowInvalidDataContractException(String message, Type type) at System.Runtime.Serialization.DataContract.DataContractCriticalHelper.CreateDataContract(Int32 id, RuntimeTypeHandle typeHandle, Type type) at System.Runtime.Serialization.DataContract.DataContractCriticalHelper.GetDataContractSkipValidation(Int32 id, RuntimeTypeHandle typeHandle, Type type) at System.Runtime.Serialization.XsdDataContractExporter.GetSchemaTypeName(Type type) at System.ServiceModel.Dispatcher.DataContractSerializerOperationFormatter.ValidateDataContractType(Type type) at System.ServiceModel.Dispatcher.DataContractSerializerOperationFormatter.CreatePartInfo(MessagePartDescription part, OperationFormatStyle style, DataContractSerializerOperationBehavior serializerFactory) at System.ServiceModel.Dispatcher.DataContractSerializerOperationFormatter.CreateMessageInfo(DataContractFormatAttribute dataContractFormatAttribute, MessageDescription messageDescription, DataContractSerializerOperationBehavior serializerFactory) at System.ServiceModel.Dispatcher.DataContractSerializerOperationFormatter..ctor(OperationDescription description, DataContractFormatAttribute dataContractFormatAttribute, DataContractSerializerOperationBehavior serializerFactory) at System.ServiceModel.Description.DataContractSerializerOperationBehavior.GetFormatter(OperationDescription operation, Boolean& formatRequest, Boolean& formatReply, Boolean isProxy) at System.ServiceModel.Description.DataContractSerializerOperationBehavior.System.ServiceModel.Description.IOperationBehavior.ApplyDispatchBehavior(OperationDescription description, DispatchOperation dispatch) at System.ServiceModel.Description.DispatcherBuilder.BindOperations(ContractDescription contract, ClientRuntime proxy, DispatchRuntime dispatch) at System.ServiceModel.Description.DispatcherBuilder.InitializeServiceHost(ServiceDescription description, ServiceHostBase serviceHost) at System.ServiceModel.ServiceHostBase.InitializeRuntime() at System.ServiceModel.ServiceHostBase.OnBeginOpen() at System.ServiceModel.ServiceHostBase.OnOpen(TimeSpan timeout) at System.ServiceModel.Channels.CommunicationObject.Open(TimeSpan timeout) at System.ServiceModel.Channels.CommunicationObject.Open() at Microsoft.Tools.SvcHost.ServiceHostHelper.OpenService(ServiceInfo info)

As requested here is the DLL containing Transaction:

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

namespace SharedLibrary
{
    // Transaction class to encapsulate products and checkout data
    public class Transaction
    {
            public int checkoutID;
            public DateTime time;
            public List<object> products; // Using object to avoid MarketService reference, remember to cast back!
            public double totalPrice;
            public bool complete;

            public Transaction(int ID)
            {
                checkoutID = ID;
            }

            public void Start()
            {
                products = new List<object>();
                complete = false;
            }

            public void Complete()
            {
                time = DateTime.Now;
                complete = true;
            }
        }
}

Thanks.

Answer 1

Do I have to mark the Transaction class here with [attribute] headers?

No, you shouldn't have to, but it is recommended. See Using Data Contracts.

---

The problem is that you are passing derived objects in a List<object>.

You have to tell the service what type objects to handle with a ServiceKnownType attribute:

[OperationContract]
[ServiceKnownType( typeof( MarketService.XXX ) )]
bool ProcessTransaction(SharedLibrary.Transaction transaction);