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Programming WCF Services by Juval Lowy

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Data Contract Hierarchy

Your data contract class may be the subclass of another data contract class. WCF requires that every level in the class hierarchy explicitly opt in for a given data contract, because the DataContract attribute is not inheritable:

[DataContract]
class Contact
{
   [DataMember]
   public string FirstName;

   [DataMember]
   public string LastName;
}[DataContract]
class Customer : Contact
{
   [DataMember]
   public int OrderNumber;
}

Failing to designate every level in the class hierarchy as serializable or as a data contract will result in an InvalidDataContractException at the service load time. WCF lets you mix the Serializable and DataContract attribute in the class hierarchy:

[Serializable]
class Contact
{...}

[DataContract]
class Customer : Contact
{..}

But typically the Serializable attribute will be at the root of the class hierarchy, if at all, because new classes should use the DataContract attribute. When you export a data contract hierarchy, the metadata maintains the hierarchy, and all levels of the class hierarchy are exported when making use of the subclass in a service contract:

[ServiceContract]
interface IContactManager
{
   [OperationContract]
   void AddCustomer(Customer customer);//Contact is exported as well
   ...
}

Known Types

While languages such as C# let you substitute a subclass for a base class, this is not the case with WCF operations. By default, you cannot use a subclass of a data contract class instead of its base class. Consider this service contract:

[ServiceContract] ...

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