How can you control .NET DataContract serialization so it uses XML attributes instead of elements?

Question

If I have a class marked as a DataContract and a few properties on it marked with DataMember attributes I can serialize it out to XML easily, but it would create output like:

<Person>
    <Name>John Smith</Name>
    <Email>[email protected]</Email>
    <Phone>123-123-1234</Phone>
</Person>

What I would prefer is attributes, like...

<Person Name="John Smith" Email="[email protected]" Phone="123-123-1234" />

The DataMember attribute allows me to control the Name and Order but not whether it is serialized as an element or attribute. I have looked around and found DataContractFormat and IXmlSerializable but I am hoping there is there an easier solution.

What is the easiest way to do this?

Answer 1

You can do this with the DataContractSerializer - the answer is to take over the Xml serialization yourself by implementing the IXmlSerializable interface. For write-only support - you can leave the implementation of ReadXml empty, and return null for GetSchema, and then write the implementation of WriteXml as follows:

public class MyPerson : IXmlSerializable
{
  public string Name { get; set;}
  public string Email { get; set;}
  public string Phone { get; set;}

  public XmlSchema GetSchema() { return null; }
  public void ReadXml(XmlReader reader) { }
  public void WriteXml(XmlWriter writer)
  { 
    writer.WriteAttributeString("name", Name);
    writer.WriteAttributeString("email", Email);
    writer.WriteAttributeString("phone", Phone);
  } 
}

If you're using the same type for, say, JSON serialization as well, then you are still free to add the DataContract and DataMember attributes - the DataContractSerializer will utilise the IXmlSerializable interface implementation only when writing Xml.

I blogged about this here.

Answer 2

You can't do this with the DataContractSerializer; if you want attributes you need to use the XmlSerializer instead. With the DataContractSerializer class a more restrictive subset of the XML specification is permitted which improves performance, and improves the interoperability of published services, but gives you rather less control over the XML format.

If you're using WCF services then take a look at XmlSerializerFormatAttribute which allows you to use the XmlSerializer for serialization.