XML attribute not getting namespace prefix

Question

I need to generate the following XML during serialization: (fragment)

<IncidentEvent a:EventTypeText="Beginning" xmlns:a="http://foo">
  <EventDate>2013-12-18</EventDate>
  <EventTime>00:15:28</EventTime>
</IncidentEvent>

The class in question looks like this:

public class IncidentEvent
{
    public string EventDate { get; set; }
    public string EventTime { get; set; }

    [XmlAttribute("EventTypeText", Namespace = "http://foo")]
    public string EventTypeText { get; set; }

}

It appears that the serializer is noticing that the namespace is already declared in an xmlns: at the root and is ignoring my attribute. I also tried the following:

[XmlRoot(Namespace = "http://foo")]
public class IncidentEvent
{
    public string EventDate { get; set; }
    public string EventTime { get; set; }

    private XmlSerializerNamespaces _Xmlns;

    [XmlNamespaceDeclarations]
    public XmlSerializerNamespaces Xmlns
    {
        get
        {
            if (_Xmlns == null)
            {
                _Xmlns = new XmlSerializerNamespaces();
                _Xmlns.Add("ett", "http://foo");
            }

            return _Xmlns;
        }

        set
        {
            _Xmlns = value;
        }
    }


    [XmlAttribute("EventTypeText", Namespace = "http://foo")]
    public string EventTypeText { get; set; }

}

This results in the following XML:

  <ett:IncidentEvent EventTypeText="Beginning" xmlns:ett="http://foo">
    <ett:EventDate>2013-12-18</ett:EventDate>
    <ett:EventTime>00:15:28</ett:EventTime>
  </ett:IncidentEvent>

Which is not what I want. The element shouldn't be prefixed, the attribute should be. What is needed to get the serializer to understand what I want?

Answer 1

I did some research may be following answer helps

For Attributes to have namespace prefix you have to specify a different namespace tag other than what you have specified http://foo. Following code hopefully will solve your issue. In the code i have remove the namespace for elements and added only for the attribute.

public class IncidentEvent
{
    public string EventDate { get; set; }
    public string EventTime { get; set; }

    [XmlAttribute("EventTypeText", Namespace = "http://foo")]
    public string EventTypeText { get; set; }

}

class Program
{
    static void Main(string[] args)
    {
        IncidentEvent xmlObj = new IncidentEvent()
        {
            EventDate = "2012.12.01",
            EventTime = "1:00:00",
            EventTypeText = "Beginining"
        };
        XmlSerializerNamespaces ns = new XmlSerializerNamespaces();
        ns.Add("ett", "http://foo");
        XmlSerializer serializer = new XmlSerializer(typeof(IncidentEvent));
        serializer.Serialize(Console.OpenStandardOutput(), xmlObj, ns);
        Console.WriteLine();
    }
}

http://www.w3.org/TR/2009/REC-xml-names-20091208/#defaulting

Answer 2

This may be a bug in XmlSerializer.

As you have noticed, even when XmlAttributeAttribute.Namespace is set explicitly, the attribute will not be prefixed in certain situations. From testing, this appears to happen when the attribute namespace happens to be the same as the namespace of the element currently being written.

For instance:

[XmlRoot(Namespace = "http://foo")]
public class IncidentEvent
{
    [XmlAttribute("EventTypeText", Namespace = "http://foo")]
    public string EventTypeText { get; set; }
}

Serializes to the following XML:

<q1:IncidentEvent EventTypeText="an attribute" xmlns:q1="http://foo" />

And since the attribute is unprefixed, it's actually not in any namespace, as is explained in the XML standard: The namespace name for an unprefixed attribute name always has no value.

However, the following:

[XmlRoot(Namespace = "http://foo")]
public class IncidentEvent
{
    [XmlAttribute("EventTypeText", Namespace = "http://bar")]
    public string EventTypeText { get; set; }
}

Serializes with the attribute correctly prefixed:

<q1:IncidentEvent p1:EventTypeText="an attribute" xmlns:p1="http://bar" xmlns:q1="http://foo" />

The workaround is to explicitly set [XmlAttribute(Form = XmlSchemaForm.Qualified)]. Thus:

[XmlRoot(Namespace = "http://foo")]
public class IncidentEvent
{
    [XmlAttribute("EventTypeText", Namespace = "http://foo", Form = XmlSchemaForm.Qualified)]
    public string EventTypeText { get; set; }
}

Serializes to

<q1:IncidentEvent q1:EventTypeText="an attribute" xmlns:q1="http://foo" />

as required.

Answer 3

Namespaces are meant to differentiate between two XML element having same name. As different XML elements can have same attribute name but different meaning. So there is no advantage of having namespace tag for an attribute as XML attributes are considered to be part of "element namespace" only. In your example

<ett:IncidentEvent EventTypeText="Beginning" xmlns:ett="http://foo">
    <ett:EventDate>2013-12-18</ett:EventDate>
    <ett:EventTime>00:15:28</ett:EventTime>
</ett:IncidentEvent>

EventTypeText is part of namespace ett:IncidentEvent Please refer to http://www.w3.org/TR/REC-xml-names/ for XML Namespaces

Answer 4

I'll give KKD credit for the answer, but I discovered another scenario that still causes issues. Apparently if the object to be serialized is a child of another object, if the parent object's namespace is the same as the child's, the serializer assumes you don't need to explicitly declare the namespace for the child.

 public class IncidentEvent : IXmlSerializable
 {
    public string EventDate { get; set; }
    public string EventTime { get; set; }
    public string EventTypeText { get; set; }

    public System.Xml.Schema.XmlSchema GetSchema()
    {
        return null;
    }

    public void ReadXml(System.Xml.XmlReader reader)
    {
        return null;
    }

    public void WriteXml(System.Xml.XmlWriter writer)
    {
        writer.WriteAttributeString("ex", "EventTypeText", "http://foo", EventTypeText);
    }
 }

By implementing IXmlSerializable, I can manually write out the elements and attributes in exactly the way I need. Since this is a one-way export, I didn't need to implement anything but the WriteXml method.

I'm still not sure if this is the best way, but it works for the moment.