What's the point of a DataContract in WCF?

Question

VS.net creates a template when you create a WCF project.

It adds a class to the iService1.cs file:

// Use a data contract as illustrated in the sample below to // add composite types to service operations. [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; }     } } 

Since a WCF service can return any user defined class, why use a DataContract and CompositeType class?

I can return something like:

 [OperationContract] MyUserCollection GetUsers(); 

What am I missing?

Answer 1

The DataContract is just a formal definition of a type that can be understood on both sides of the service boundary.

If you return, as in your example, a "MyUserCollection" object, the consumers of your service will need to reference the innards of your service/system, which is a violation of the SOA tenet of explicit boundaries. By using a DataContract, you are publishing the structure of your return types in a loosely-coupled way.