What is the use of [KnownType] attribute in WCF?

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ICSM Computer · Answer

The [KnownType] attribute in WCF is used to inform the DataContractSerializer about derived or related types that might be encountered during serialization or deserialization of a base type.
Why [KnownType] is Needed
By default, WCF only serializes types it knows about — those marked with 
[DataContract] and explicitly referenced. If a service operation uses a 
base class or interface as a parameter or return type, WCF needs to know in advance about all
possible derived types.
Without [KnownType], WCF will throw a serialization error when it encounters an unknown derived type at runtime.
Example Scenario
Suppose you have a base class Shape and two derived classes 
Circle and Square.
[DataContract]
[KnownType(typeof(Circle))]
[KnownType(typeof(Square))]
public abstract class Shape
{
    [DataMember]
    public string Color { get; set; }
}
[DataContract]
public class Circle : Shape
{
    [DataMember]
    public double Radius { get; set; }
}
[DataContract]
public class Square : Shape
{
    [DataMember]
    public double SideLength { get; set; }
}
Now you can safely use Shape as a parameter or return type in your service contract:
[ServiceContract]
public interface IShapeService
{
    [OperationContract]
    void SaveShape(Shape shape);
}
WCF will correctly serialize and deserialize Circle or Square when passed as a
Shape.
Alternate Form of KnownType
You can also declare known types through a method:
[KnownType("GetKnownTypes")]
public abstract class Shape
{
    public static Type[] GetKnownTypes()
    {
        return new Type[] { typeof(Circle), typeof(Square) };
    }
}
This is useful if known types are determined dynamically.
Summary
[KnownType] helps WCF handle polymorphism during serialization.Required when base types may be substituted with derived types at runtime.Prevents runtime errors during service communication involving inheritance.

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What is the use of [KnownType] attribute in WCF?

ICSM Computer

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Why `[KnownType]` is Needed

Example Scenario

Alternate Form of KnownType

Summary

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