Question

could some one please confirm whether I should always have a DataContract and datamember attribute for Operation Parameter and return types?
e.g.

ResponseMessage getOrderDetails(RequestMessage msg)
{
  ....
}


public class ResponseMessage
{
  ...
}


public class RequestMessage
{
  ...
}

Answer 1

The parameter types and return types need to be either serializable or treated in a special way by WCF.

For the first case, [DataContract] and [DataMember] is only one way to make a type serializable – the post at http://blogs.msdn.com/b/sowmy/archive/2006/02/22/536747.aspx describes the serialization programming model in WCF. As Ladislav mentioned, starting with .NET 3.5 SP1 WCF introduced a default (POCO) serialization so you don’t need any annotation at all.

For the second case, there are some types which are treated as special cases by WCF, such as System.IO.Stream or System.ServiceModel.Channels.Message – and you can even add more such types if you use a custom message formatter (although this is an advanced scenario and not very common).