Remove empty xmlns created by serializer

Question

I have an object generated by an "Add service reference..." operation and I am manually serializing it with a generic serializer I wrote.

My problem is that the data contract has some internal objects.

The serializer adds an empty namespace atribute to the starting tag of the internal objects. Is there any way to stop this from happening?

Answer 1

What about making your internal objects belong to the same namespace as the root? That way, it would be correct to omit the xmlns declaration from the descendants. You can use the [assembly: ContractNamespace] attribute to override the namespace for all contracts in your assembly. Refer to Data Contract Names for an example.

Edit: An elaboration with some examples below.

Suppose you’re constructing an XML document manually, and don’t specify a namespace for any of your elements.

XDocument xmlDocument = new XDocument(
    new XElement("Book",
        new XElement("Title", "Animal Farm"),
        new XElement("Author", "George Orwell"),
        new XElement("Publisher",
            new XElement("Name", "Secker and Warburg"),
            new XElement("Location", "London"),
            new XElement("Founded", 1910))));
return xmlDocument.ToString();

The generated XML would, as expected, be void of namespace declarations:

<Book>
  <Title>Animal Farm</Title>
  <Author>George Orwell</Author>
  <Publisher>
    <Name>Secker and Warburg</Name>
    <Location>London</Location>
    <Founded>1910</Founded>
  </Publisher>
</Book>

If, however, you specify a namespace just for your root element, then all child elements must explicitly revert out of that default namespace, using the xml="" declaration. Per the Namespace Defaulting rules:

The scope of a default namespace declaration extends from the beginning of the start-tag in which it appears to the end of the corresponding end-tag, excluding the scope of any inner default namespace declarations. In the case of an empty tag, the scope is the tag itself.

Thus, the following code (having a namespace specified for the root element)…

XDocument xmlDocument = new XDocument(
    new XElement("{http://example.com/library}Book",
        new XElement("Title", "Animal Farm"),
        new XElement("Author", "George Orwell"),
        new XElement("Publisher",
            new XElement("Name", "Secker and Warburg"),
            new XElement("Location", "London"),
            new XElement("Founded", 1910))));
return xmlDocument.ToString();

…would give the following XML:

<Book xmlns="http://example.com/library">
  <Title xmlns="">Animal Farm</Title>
  <Author xmlns="">George Orwell</Author>
  <Publisher xmlns="">
    <Name>Secker and Warburg</Name>
    <Location>London</Location>
    <Founded>1910</Founded>
  </Publisher>
</Book>

Note how the children of the <Publisher> element do not need to revert out of the root’s namespace, since they inherit the “no namespace” declaration from their parent.

To eliminate the xmlns="" declarations, we could, for the sake of the demonstration, assign the same namespace to all descendants:

XDocument xmlDocument = new XDocument(
    new XElement("{http://example.com/library}Book",
        new XElement("{http://example.com/library}Title", "Animal Farm"),
        new XElement("{http://example.com/library}Author", "George Orwell"),
        new XElement("{http://example.com/library}Publisher",
            new XElement("{http://example.com/library}Name", "Secker and Warburg"),
            new XElement("{http://example.com/library}Location", "London"),
            new XElement("{http://example.com/library}Founded", 1910))));
return xmlDocument.ToString();

This would give an XML document with the namespace declared in just the root (and implicitly inherited in all descendants):

<Book xmlns="http://example.com/library">
  <Title>Animal Farm</Title>
  <Author>George Orwell</Author>
  <Publisher>
    <Name>Secker and Warburg</Name>
    <Location>London</Location>
    <Founded>1910</Founded>
  </Publisher>
</Book>

To mimic your scenario involving a web service, we can create the following WCF service.

[DataContract]
public class Book
{
    [DataMember]
    public string Title { get; set; }
    [DataMember]
    public string Author { get; set; }
    [DataMember]
    public Publisher Publisher { get; set; }
}

[DataContract]
public class Publisher
{
    [DataMember]
    public string Name { get; set; }
    [DataMember]
    public string Location { get; set; }
    [DataMember]
    public short Founded { get; set; }
}

[ServiceContract]
public interface ILibraryService
{
    [OperationContract]
    Book GetBook();
}

public class LibraryService : ILibraryService
{
    public Book GetBook()
    {
        return new Book
        {
            Title = "Animal Farm",
            Author = "George Orwell",
            Publisher = new Publisher
            {
                Name = "Secker and Warburg",
                Location = "London",
                Founded = 1910,
            }
        };
    }
}

We add a service reference to the above service in our client application, consume its operation, and serialize the result whilst enclosing it in a root Books element having an explicit namespace:

using (var libraryClient = new LibraryServiceReference.LibraryServiceClient())
{
    var book = libraryClient.GetBook();

    var stringBuilder = new StringBuilder();
    using (XmlWriter xmlWriter = XmlWriter.Create(stringBuilder))
    {
        xmlWriter.WriteStartElement("Books", "http://example.com/library");
        var serializer = new XmlSerializer(book.GetType());
        serializer.Serialize(xmlWriter, book);
        xmlWriter.WriteEndElement();
    }

    return stringBuilder.ToString();
}

In this case, the inner element Book contains an xmlns="" declaration.

<?xml version="1.0" encoding="utf-16"?>
<Books xmlns="http://example.com/library">
  <Book xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
        xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
        xmlns="">
    <ExtensionData />
    <Author>George Orwell</Author>
    <Publisher>
      <ExtensionData />
      <Founded>1910</Founded>
      <Location>London</Location>
      <Name>Secker and Warburg</Name>
    </Publisher>
    <Title>Animal Farm</Title>
  </Book>
</Books>

As explained above, this xmlns="" can be eliminated by setting the Book element’s namespace (and that of its descendants) to correspond to the root’s. For the XmlSerializer class, the default namespace for all elements can be specified through the second parameter to its constructor. (The actual technique would vary depending on which serialization strategy you’re using.)

using (var libraryClient = new LibraryServiceReference.LibraryServiceClient())
{
    var book = libraryClient.GetBook();

    var stringBuilder = new StringBuilder();
    using (XmlWriter xmlWriter = XmlWriter.Create(stringBuilder))
    {
        xmlWriter.WriteStartElement("Books", "http://example.com/library");
        var serializer = new XmlSerializer(book.GetType(), "http://example.com/library");
        serializer.Serialize(xmlWriter, book);
        xmlWriter.WriteEndElement();
    }

    return stringBuilder.ToString();
}

And that would give the expected result:

<?xml version="1.0" encoding="utf-16"?>
<Books xmlns="http://example.com/library">
  <Book xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
        xmlns:xsd="http://www.w3.org/2001/XMLSchema">
    <ExtensionData />
    <Author>George Orwell</Author>
    <Publisher>
      <ExtensionData />
      <Founded>1910</Founded>
      <Location>London</Location>
      <Name>Secker and Warburg</Name>
    </Publisher>
    <Title>Animal Farm</Title>
  </Book>
</Books>