Imports System
Imports System.IO
Imports System.Collections
Imports System.Collections.Generic
Imports System.Runtime.Serialization
Imports ServiceStack
Imports ServiceStack.DataAnnotations
Imports Test.ServiceInterface
Imports Test.ServiceModel
Imports Test.ServiceModel.Types
Namespace Global
    Namespace ServiceStack
        <DataContract>
        Public Partial Class QueryBase
            <DataMember(Order:=1)>
            Public Overridable Property Skip As Integer?
            <DataMember(Order:=2)>
            Public Overridable Property Take As Integer?
            <DataMember(Order:=3)>
            Public Overridable Property OrderBy As String
            <DataMember(Order:=4)>
            Public Overridable Property OrderByDesc As String
            <DataMember(Order:=5)>
            Public Overridable Property Include As String
            <DataMember(Order:=6)>
            Public Overridable Property Fields As String
            <DataMember(Order:=7)>
            Public Overridable Property Meta As Dictionary(Of String, String)
        End Class
        Public Partial Class QueryDb(Of From, Into)
            Inherits QueryBase
        End Class
        <DataContract>
        Public Partial Class QueryResponse(Of T)
            <DataMember(Order:=1)>
            Public Overridable Property Offset As Integer
            <DataMember(Order:=2)>
            Public Overridable Property Total As Integer
            <DataMember(Order:=3)>
            Public Overridable Property Results As List(Of Poco) = New List(Of Poco)
            <DataMember(Order:=4)>
            Public Overridable Property Meta As Dictionary(Of String, String)
            <DataMember(Order:=5)>
            Public Overridable Property ResponseStatus As ResponseStatus
        End Class
    End Namespace
    Namespace Test.ServiceInterface
        Public Partial Class QueryItems
            Inherits QueryDb(Of Item, Poco)
        End Class
    End Namespace
    Namespace Test.ServiceModel
        Public Partial Class Item
            Public Overridable Property Name As String
            Public Overridable Property Description As String
        End Class
    End Namespace
    Namespace Test.ServiceModel.Types
        Public Partial Class Poco
            Public Overridable Property Name As String
        End Class
    End Namespace
End Namespace
To override the Content-type in your clients, use the HTTP Accept Header, append the .xml suffix or ?format=xml
The following are sample HTTP requests and responses. The placeholders shown need to be replaced with actual values.
POST /xml/reply/QueryItems HTTP/1.1 
Host: test.servicestack.net 
Accept: application/xml
Content-Type: application/xml
Content-Length: length
<QueryItems xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.datacontract.org/2004/07/Test.ServiceInterface">
  <Skip xmlns="http://schemas.servicestack.net/types">0</Skip>
  <Take xmlns="http://schemas.servicestack.net/types">0</Take>
  <OrderBy xmlns="http://schemas.servicestack.net/types">String</OrderBy>
  <OrderByDesc xmlns="http://schemas.servicestack.net/types">String</OrderByDesc>
  <Include xmlns="http://schemas.servicestack.net/types">String</Include>
  <Fields xmlns="http://schemas.servicestack.net/types">String</Fields>
  <Meta xmlns:d2p1="http://schemas.microsoft.com/2003/10/Serialization/Arrays" xmlns="http://schemas.servicestack.net/types">
    <d2p1:KeyValueOfstringstring>
      <d2p1:Key>String</d2p1:Key>
      <d2p1:Value>String</d2p1:Value>
    </d2p1:KeyValueOfstringstring>
  </Meta>
</QueryItems>
HTTP/1.1 200 OK
Content-Type: application/xml
Content-Length: length
<QueryResponseOfPocoasRYHj6T xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.servicestack.net/types">
  <Offset>0</Offset>
  <Total>0</Total>
  <Results xmlns:d2p1="http://schemas.datacontract.org/2004/07/Test.ServiceModel.Types">
    <d2p1:Poco>
      <d2p1:Name>String</d2p1:Name>
    </d2p1:Poco>
  </Results>
  <Meta xmlns:d2p1="http://schemas.microsoft.com/2003/10/Serialization/Arrays">
    <d2p1:KeyValueOfstringstring>
      <d2p1:Key>String</d2p1:Key>
      <d2p1:Value>String</d2p1:Value>
    </d2p1:KeyValueOfstringstring>
  </Meta>
  <ResponseStatus>
    <ErrorCode>String</ErrorCode>
    <Message>String</Message>
    <StackTrace>String</StackTrace>
    <Errors>
      <ResponseError>
        <ErrorCode>String</ErrorCode>
        <FieldName>String</FieldName>
        <Message>String</Message>
        <Meta xmlns:d5p1="http://schemas.microsoft.com/2003/10/Serialization/Arrays">
          <d5p1:KeyValueOfstringstring>
            <d5p1:Key>String</d5p1:Key>
            <d5p1:Value>String</d5p1:Value>
          </d5p1:KeyValueOfstringstring>
        </Meta>
      </ResponseError>
    </Errors>
    <Meta xmlns:d3p1="http://schemas.microsoft.com/2003/10/Serialization/Arrays">
      <d3p1:KeyValueOfstringstring>
        <d3p1:Key>String</d3p1:Key>
        <d3p1:Value>String</d3p1:Value>
      </d3p1:KeyValueOfstringstring>
    </Meta>
  </ResponseStatus>
</QueryResponseOfPocoasRYHj6T>