Tuesday, 28 April 2015

WCF Service – KnownType DataContract

Data Contract describes the type of data that will be sent or received between a service and a client. But in certain scenarios, sent or received data is not known between the the communicating parties. For example, a service sending data back to client is not the actual data contract but a derived type of it. In such cases, there will be a De-serialization problem. De-serialization engine will not recognize the derived Data Contract type and will generate an error.
In order to handle such scenarios, Data Contract Known types are available in Windows Communication Foundation. So by definition, “Known Type in WCF is an acceptable derived type for a Data Contract“.In one of the article WCF Service articles, blogger explained WCF KnowTypeAttribute with the help of a simple example. But here in this WCF Tutorial, I’ll try to discuss all possible ways to use Data Contract Known Types, so that the reader can get a detailed understanding about Known Types and be able to use it in various practical scenarios.

Consider the following Data Contract classes having inheritance relationship as follows:


    [DataContract]
    public class UserAccount { }

    [DataContract]
    public class Admin : UserAccount { }

    [DataContract]

    public class Guest : UserAccount { }

Now, look into following code:

    [DataContract]
    [ServiceKnownType(typeof(Admin))]
    [ServiceKnownType(typeof(Guest))]
    public class SecurityInfo
    {
        [DataMember]
        private UserAccount user;
    }

Above code will work fine, either we set SecurityInfo data member to Admin or Guest.
But if KnownTypeAttribute for Admin and Guest are not provided, deserialization engine will not recognize Admin and Guest types and will cry.
For more detailed understanding with example of all possible ways of associating Known Types in WCF, Click Here.

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