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IDataContractSurrogate Interface

Provides the methods needed to substitute one type for another by the DataContractSerializer during serialization, deserialization, and export and import of XML schema documents (XSD).

Namespace:  System.Runtime.Serialization
Assembly:  System.Runtime.Serialization (in System.Runtime.Serialization.dll)

'Declaration
Public Interface IDataContractSurrogate
'Usage
Dim instance As IDataContractSurrogate

Use the IDataContractSurrogate when using the DataContractSerializer if you need to do one of the following: substitute one type or object for another, or to dynamically generate schema variations. For a sample application, see DataContract Surrogate Sample. For more information about data contracts, see Using Data Contracts.

At run time, you can find the specific DataContractSerializer for any operation in a service by using the OperationDescription to find the DataContractSerializerOperationBehavior instance. For more information about implementing the interface to create a surrogate, see Data Contract Surrogates.

You can also use the IDataContractSurrogate to affect the import and export of XML schemas when you are using the XsdDataContractExporter and XsdDataContractImporter classes. You can do so by assigning the IDataContractSurrogate to the DataContractSurrogate property of the ExportOptions class, or to the DataContractSurrogate property of the ImportOptions class. For more information, see Schema Import and Export.

The following example shows an implementation of the IDataContractSurrogate interface. The code substitutes the serialization of the Person type for a PersonSurrogated class.

Class Program

    Shared Sub Main(ByVal args() As String) 
        ' Create and populate an Employee instance. 
        Dim emp As New Employee()
        emp.date_hired = New DateTime(1999, 10, 14)
        emp.salary = 33000

        ' Note that the Person class is a legacy XmlSerializable class 
        ' without a DataContract.
        emp.person = New Person()
        emp.person.first_name = "Mike"
        emp.person.last_name = "Ray"
        emp.person.age = 44

        ' Create a serializer. 
        Dim ser As New DataContractSerializer(GetType(Employee))

        ' Attempt to serialize without a surrogate. (This will fail.)
        Console.WriteLine(" Attempting to serialize without a surrogate: " + vbLf)
        Dim fileName As String = "surrogateEmployee.xml" 
        Dim fs As New FileStream(fileName, FileMode.Create)
        Dim writer As XmlDictionaryWriter = XmlDictionaryWriter.CreateTextWriter(fs)
        Try
            ser.WriteObject(writer, emp)
            writer.Flush()
            writer.Close()
        Catch 
            writer.Flush()
            Console.Write(writer.ToString())
            Console.WriteLine(vbLf + vbLf + _
          " Cannot serialize without a surrogate since Person has no DataContract " + vbLf)
        End Try 
        ' Close the writer objects after failing to serialize.
        writer.Close()
        fs.Close()

        Console.WriteLine(" Now use a surrogate for the Person class and try again")
        ' Create a new instance of the serializer. The  
        ' constructor demands a knownTypes and surrogate.  
        ' Create a Generic List for the knownTypes. Then create an 
        ' instance of the surrogate class (defined below). 
        Dim knownTypes As List(Of Type) = New List(Of Type)()
        Dim sur As New LegacyPersonTypeSurrogate()
        Dim surrogateSerializer As New _
        DataContractSerializer(GetType(Employee), _
           knownTypes, Integer.MaxValue, False, True, sur)

        ' Create a new writer. Then serialize with the  
        ' surrogate serializer. 
        Dim newFs As New FileStream(fileName, FileMode.Create)
        Dim newWriter As XmlDictionaryWriter = XmlDictionaryWriter.CreateTextWriter(newFs)
        Try
            surrogateSerializer.WriteObject(newWriter, emp)
            Console.Write(newWriter.ToString())
            Console.WriteLine("Serialization succeeded. Now doing deserialization.")
            newWriter.Close()
            newFs.Close()
        Catch 
            Console.WriteLine(" We never get here")
        End Try 

        ' Create a new reader object. 
        Dim fs2 As New FileStream(fileName, FileMode.Open)
        Dim reader As XmlDictionaryReader = _
            XmlDictionaryReader.CreateTextReader(fs2, New XmlDictionaryReaderQuotas())

        Console.WriteLine("Trying to deserialize with surrogate.")
        Try 
            Dim newemp As Employee = CType _
                (surrogateSerializer.ReadObject(reader, False), Employee)

            reader.Close()
            fs2.Close()

            Console.WriteLine("Deserialization succeeded. " + vbLf + vbLf)
            Console.WriteLine("Deserialized Person data: " + vbLf + vbTab + _
                " {0} {1}", newemp.person.first_name, newemp.person.last_name)
            Console.WriteLine(vbTab + " Age: {0} " + vbLf, newemp.person.age)

        Catch serEx As SerializationException
            Console.WriteLine(serEx.Message)
            Console.WriteLine(serEx.StackTrace)
        End Try

        Console.WriteLine("Now doing schema export/import.")

        ' The following code demonstrates schema export with a surrogate. 
        ' The surrogate indicates how to export the non-DataContract Person type. 
        ' Without the surrogate, schema export would fail. 
        Dim xsdexp As New XsdDataContractExporter()
        xsdexp.Options = New ExportOptions()
        xsdexp.Options.DataContractSurrogate = New LegacyPersonTypeSurrogate()
        xsdexp.Export(GetType(Employee))

        ' Write out the exported schema to a file. 
        Dim fs3 As New FileStream("sample.xsd", FileMode.Create)
        Try 
            Dim sch As XmlSchema
            For Each sch In xsdexp.Schemas.Schemas()
                sch.Write(fs3)
            Next sch
        Finally
            fs3.Dispose()
        End Try 

        ' The following code demonstrates schema import with  
        ' a surrogate. The surrogate is used to indicate that  
        ' the Person class already exists and that there is no  
        ' need to generate a new class when importing the 
        ' PersonSurrogated data contract. If the surrogate  
        ' was not used, schema import would generate a  
        ' PersonSurrogated class, and the person field  
        ' of Employee would be imported as  
        ' PersonSurrogated and not Person. 
        Dim xsdimp As New XsdDataContractImporter()
        xsdimp.Options = New ImportOptions()
        xsdimp.Options.DataContractSurrogate = New LegacyPersonTypeSurrogate()
        xsdimp.Import(xsdexp.Schemas)

        ' Write out the imported schema to a C-Sharp file. 
        Dim fs4 As FileStream = New FileStream("sample.cs", FileMode.Create)
        Try 
            Dim tw As New StreamWriter(fs4)
            Dim cdp As New Microsoft.CSharp.CSharpCodeProvider()
            cdp.GenerateCodeFromCompileUnit(xsdimp.CodeCompileUnit, tw, Nothing)
            tw.Flush()
        Finally
            fs4.Dispose()
        End Try

        Console.WriteLine(vbLf + " To see the results of schema export and import,")
        Console.WriteLine(" see SAMPLE.XSD and SAMPLE.CS." + vbLf)

        Console.WriteLine(" Press ENTER to terminate the sample." + vbLf)
        Console.ReadLine()

    End Sub  
End Class  


' This is the Employee (outer) type used in the sample.

<DataContract()>  _
Class Employee
    <DataMember()>  _
    Public date_hired As DateTime

    <DataMember()>  _
    Public salary As [Decimal]

    <DataMember()>  _
    Public person As Person
End Class  


' This is the Person (inner) type used in the sample. 
' Note that it is a legacy XmlSerializable type and not a DataContract type. 

Public Class Person
    <XmlElement("FirstName")>  _
    Public first_name As String

    <XmlElement("LastName")>  _
    Public last_name As String

    <XmlAttribute("Age")>  _
    Public age As Integer 


    Public Sub New() 

    End Sub  
End Class  

' This is the surrogated version of the Person type 
' that will be used for its serialization/deserialization.

<DataContract()>  _
Class PersonSurrogated

    ' xmlData will store the XML returned for a Person instance  
    ' by the XmlSerializer.
    <DataMember()>  _
    Public xmlData As String 

End Class  



' This is the surrogate that substitutes PersonSurrogated for Person. 

Class LegacyPersonTypeSurrogate 
Implements IDataContractSurrogate

    Public Function GetDataContractType(ByVal type As Type) As Type _
       Implements IDataContractSurrogate.GetDataContractType

        ' "Person" will be serialized as "PersonSurrogated" 
        ' This method is called during serialization, 
        ' deserialization, and schema export. 
        If GetType(Person).IsAssignableFrom(type) Then 
            Return GetType(PersonSurrogated)
        End If 
        Return type

    End Function  

    Public Function GetObjectToSerialize(ByVal obj As Object, _
        ByVal targetType As Type) As Object _
        Implements IDataContractSurrogate.GetObjectToSerialize

        ' This method is called on serialization. 
        ' If Person is not being serialized... 
        If TypeOf obj Is Person Then 
            ' ... use the XmlSerializer to perform the actual serialization. 
            Dim ps As New PersonSurrogated()
            Dim xs As New XmlSerializer(GetType(Person))
            Dim sw As New StringWriter()
            xs.Serialize(sw, CType(obj, Person))
            ps.xmlData = sw.ToString()
            Return ps
        End If 
        Return obj

    End Function      

    Public Function GetDeserializedObject(ByVal obj As Object, _
        ByVal targetType As Type) As Object Implements _
        IDataContractSurrogate.GetDeserializedObject

        ' This method is called on deserialization. 
        ' If PersonSurrogated is not being deserialized... 
        If TypeOf obj Is PersonSurrogated Then 
            '... use the XmlSerializer to do the actual deserialization. 
            Dim ps As PersonSurrogated = CType(obj, PersonSurrogated)
            Dim xs As New XmlSerializer(GetType(Person))
            Return CType(xs.Deserialize(New StringReader(ps.xmlData)), Person)
        End If 
        Return obj

    End Function      

    Public Function GetReferencedTypeOnImport(ByVal typeName As String, _
        ByVal typeNamespace As String, ByVal customData As Object) As Type _
        Implements IDataContractSurrogate.GetReferencedTypeOnImport

        ' This method is called on schema import. 
        ' If a PersonSurrogated data contract is  
        ' in the specified namespace, do not create a new type for it  
        ' because there is already an existing type, "Person". 

        If typeNamespace.Equals("http://schemas.datacontract.org/2004/07/DCSurrogateSample") Then 
            If typeName.Equals("PersonSurrogated") Then 
                Return GetType(Person)
            End If 
        End If 
        Return Nothing 

    End Function      

    Public Function ProcessImportedType(ByVal typeDeclaration _
        As System.CodeDom.CodeTypeDeclaration, _
        ByVal compileUnit As System.CodeDom.CodeCompileUnit) _
        As System.CodeDom.CodeTypeDeclaration _
	Implements IDataContractSurrogate.ProcessImportedType

        ' Not used in this sample. 
        ' You could use this method to construct an entirely new CLR  
        ' type when a certain type is imported, or modify a  
        ' generated type in some way. 
        Return typeDeclaration
    End Function  


    Overloads Public Function GetCustomDataToExport _
        (ByVal clrType As Type, ByVal dataContractType As Type) As Object _
        Implements IDataContractSurrogate.GetCustomDataToExport

        ' Not used in this sample 
        Return Nothing     
    End Function  


    Overloads Public Function GetCustomDataToExport _
       (ByVal memberInfo As System.Reflection.MemberInfo, _
       ByVal dataContractType As Type) As Object _
        Implements IDataContractSurrogate.GetCustomDataToExport

        ' Not used in this sample 
        Return Nothing 

    End Function  


    Public Sub GetKnownCustomDataTypes(ByVal customDataTypes As Collection(Of Type)) _
 Implements IDataContractSurrogate.GetKnownCustomDataTypes

        ' Not used in this sample 

    End Sub 
End Class

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0

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