Question

I had a WCF Service with an operation contract as

void AddQuery(IQuery Query);

My IQuery is like this

public interface IQuery
{
    Guid                Id { get; set; }        
    string              QueryNo { get; set; }
    string              Status { get; set; }
    IData               data { get; set; }
}

and the implementation of IQuery is in

[Serializable]
public class Query : IQuery
{
    Guid                Id { get; set; }        
    string              QueryNo { get; set; }
    string              Status { get; set; }
    IData               data { get; set; }
}

When i am trying to send my object from client as

  public void AddQuery(IQuery query)
  {
      try
      {
          // I am sure that the query object is not null and it is implemented
          objServiceClient.AddEnquiry(query);
      }
      catch (Exception ex)
      {
      }
  }

But i am getting an exception as

There was an error while trying to serialize parameter . The InnerException message was ‘Type ‘ViewModels.Query’ with data contract name ‘Query:http://schemas.datacontract.org/2004/07/ViewModels‘ is not expected. Consider using a DataContractResolver or add any types not known statically to the list of known types – for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer.’. Please see InnerException for more details.

Could anyone suggest me what will be the resolution for this error?

Answer 1

Consider serializing concrete classes. You cannot serialize interfaces . Refer to this answer: https://stackoverflow.com/a/4659289/860243

Some useful links I found from bing:

http://www.danrigsby.com/blog/index.php/2008/03/07/xmlserializer-vs-datacontractserializer-serialization-in-wcf/

The above article discusses your situation and examples of using [KnownType] for your derived classes

Update:

Based on this link, please check the below update:

public interface IQuery 
{ 
    Guid Id { get; set; }
    string QueryNo{ get; set; } 
    string Status { get; set; } 
    IData data {get; set;}
}

Your Query class using Data contract serializer implementing your interface IQuery

[DataContract]
public class Query : IQuery
{
    [DataMember]
    public Guid Id { get; set; };
    [DataMember]
    public string QueryNo { get; set; };
    [DataMember]
    public string Status { get; set; };
    [DataMember]
    public Data data { get; set; }; //Make sure you serialize Data class as well
}

And for your service contract:

[ServiceContract]
public interface IMyQueryService
{
      [OperationContract]
      [ServiceKnownType(typeof(Query))]
      void AddQuery(IQuery query);
}

The [ServiceKnownType(typeof(Query))] will enable your operation contract to allow Query as input. Also please note you need to specify all your IQuery implementations that needs to be passed as parameters to your Operation contract with ServiceKnownType attribute .

Also if you want more than one (or all) operation contract to take them as parameters, specify the ServiceKnownType attribute for ServiceContract instead of each operation contract separately.

Hope this helps!