Question

I am developing a WCF service designed to be consumed by non .NET clients, which performs a charge operation. I would like to be able to return either a base class DataContract or an inherited class DataContract depending on the use case.

So I have:

[DataContract]  
public class ChargeResponse  
{  
    [DataMember]  
    public string ID  

    [DataMember]  
    public string Description  
}  

For successful operations, I would like to return an inherited type having an extra DataMember such as:

[DataContract]  
public class SuccessfulChargeResponse : ChargeResponse  
{  
    [DataMember]  
    public string TransactionID  
}

For all other cases I would return the bass class. Is this possible? Or should I just have the DataMember is the base class and return an empty value.

Answer 1

You are being overly complicated – you simply need to return a ChargeResponse that contains a TransactionID. If the operation was successful TransactionID will have a value, if it wasn’t then TransactionID will be null. You can extend your class a little further to contain a flag or enumeration indicating the success, and whatever properties you need to indicate what the error was.

This is known as the request/response pattern and is quite common. Some (possibly very unexciting and not necessarily very new) links describing this:

• MSDN: Message Patterns in WCF Services
• WCF Simplified Part 2: Message Exchange Patterns (MEPs)
• Patterns for Flexible WCF Services