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IExtensibleDataObject Interface

  • Reference

Definition

Namespace:
System.Runtime.Serialization
Assembly:
System.Runtime.Serialization.Xml.dll
Assembly:
System.Runtime.Serialization.dll
Assembly:
netstandard.dll

Provides a data structure to store extra data encountered by the XmlObjectSerializer during deserialization of a type marked with the DataContractAttribute attribute.

public interface class IExtensibleDataObject
public interface IExtensibleDataObject
type IExtensibleDataObject = interface
Public Interface IExtensibleDataObject
Derived

Examples

The following code shows an instance of a type (PersonVersion2) that is the second version of a serializable type (Person). The second version contains extra data (ID field) that is not present in the first version.

// Implement the IExtensibleDataObject interface
// to store the extra data for future versions.
[DataContract(
    Name = "Person",
    Namespace = "http://www.cohowinery.com/employees")]
class Person : IExtensibleDataObject
{
    // To implement the IExtensibleDataObject interface,
    // you must implement the ExtensionData property. The property
    // holds data from future versions of the class for backward
    // compatibility.
    private ExtensionDataObject extensionDataObject_value;
    public ExtensionDataObject ExtensionData
    {
        get
        {
            return extensionDataObject_value;
        }
        set
        {
            extensionDataObject_value = value;
        }
    }
    [DataMember]
    public string Name;
}

// The second version of the class adds a new field. The field's
// data is stored in the ExtensionDataObject field of
// the first version (Person). You must also set the Name property
// of the DataContractAttribute to match the first version.
// If necessary, also set the Namespace property so that the
// name of the contracts is the same.
[DataContract(Name = "Person",
    Namespace = "http://www.cohowinery.com/employees")]
class PersonVersion2 : IExtensibleDataObject
{
    // Best practice: add an Order number to new members.
    [DataMember(Order=2)]
    public int ID;

    [DataMember]
    public string Name;

    private ExtensionDataObject extensionDataObject_value;
    public ExtensionDataObject ExtensionData
    {
        get
        {
            return extensionDataObject_value;
        }
        set
        {
            extensionDataObject_value = value;
        }
    }
}

' Implement the IExtensibleDataObject interface 
' to store the extra data for future versions.
<DataContract(Name := "Person", [Namespace] := "http://www.cohowinery.com/employees")>  _
Class Person
    Implements IExtensibleDataObject
    ' To implement the IExtensibleDataObject interface,
    ' you must implement the ExtensionData property. The property
    ' holds data from future versions of the class for backward
    ' compatibility.
    Private extensionDataObject_value As ExtensionDataObject
    
    Public Property ExtensionData() As ExtensionDataObject _
       Implements IExtensibleDataObject.ExtensionData
        Get
            Return extensionDataObject_value
        End Get
        Set
            extensionDataObject_value = value
        End Set
    End Property
    <DataMember()>  _
    Public Name As String
End Class 

' The second version of the class adds a new field. The field's 
' data is stored in the ExtensionDataObject field of
' the first version (Person). You must also set the Name property 
' of the DataContractAttribute to match the first version. 
' If necessary, also set the Namespace property so that the 
' name of the contracts is the same.

<DataContract(Name := "Person", [Namespace] := "http://www.cohowinery.com/employees")>  _
Class PersonVersion2
    Implements IExtensibleDataObject

    ' Best practice: add an Order number to new members.
    <DataMember(Order:=2)>  _
    Public ID As Integer
    
    <DataMember()>  _
    Public Name As String
    
    Private extensionDataObject_value As ExtensionDataObject
    
    Public Property ExtensionData() As ExtensionDataObject _
       Implements IExtensibleDataObject.ExtensionData
        Get
            Return extensionDataObject_value
        End Get
        Set
            extensionDataObject_value = value
        End Set
    End Property
End Class

Remarks

The IExtensibleDataObject interface provides a single property that sets or returns a structure used to store data that is external to a data contract. The extra data is stored in an instance of the ExtensionDataObject class and accessed through the ExtensionData property. In a roundtrip operation where data is received, processed, and sent back, the extra data is sent back to the original sender intact. This is useful to store data received from future versions of the contract. If you do not implement the interface, any extra data is ignored and discarded during a roundtrip operation.

To use this versioning feature

  1. Implement the IExtensibleDataObject interface in a class.

  2. Add the ExtensionData property to your type.

  3. Add a private member of type ExtensionDataObject to the class.

  4. Implement get and set methods for the property using the new private member.

  5. Apply the DataContractAttribute attribute to the class. Set the Name and Namespace properties to appropriate values if necessary.

For more information about versioning of types, see Data Contract Versioning. For information about creating forward-compatible data contracts, see Forward-Compatible Data Contracts. For more information about data contracts, see Using Data Contracts.

Properties

ExtensionData

Gets or sets the structure that contains extra data.

Applies to

See also