Omitting all xsi and xsd namespaces when serializing an object in .NET?

Question

...
XmlSerializer s = new XmlSerializer(objectToSerialize.GetType());
XmlSerializerNamespaces ns = new XmlSerializerNamespaces();
ns.Add("","");
s.Serialize(xmlWriter, objectToSerialize, ns);

This is the 2nd of two answers.

If you want to just strip all namespaces arbitrarily from a document during serialization, you can do this by implementing your own XmlWriter.

The easiest way is to derive from XmlTextWriter and override the StartElement method that emits namespaces. The StartElement method is invoked by the XmlSerializer when emitting any elements, including the root. By overriding the namespace for each element, and replacing it with the empty string, you've stripped the namespaces from the output.

public class NoNamespaceXmlWriter : XmlTextWriter
{
    //Provide as many contructors as you need
    public NoNamespaceXmlWriter(System.IO.TextWriter output)
        : base(output) { Formatting= System.Xml.Formatting.Indented;}

    public override void WriteStartDocument () { }

    public override void WriteStartElement(string prefix, string localName, string ns)
    {
        base.WriteStartElement("", localName, "");
    }
}

Suppose this is the type:

// explicitly specify a namespace for this type,
// to be used during XML serialization.
[XmlRoot(Namespace="urn:Abracadabra")]
public class MyTypeWithNamespaces
{
    // private fields backing the properties
    private int _Epoch;
    private string _Label;

    // explicitly define a distinct namespace for this element
    [XmlElement(Namespace="urn:Whoohoo")]
    public string Label
    {
        set {  _Label= value; } 
        get { return _Label; } 
    }

    // this property will be implicitly serialized to XML using the
    // member name for the element name, and inheriting the namespace from
    // the type.
    public int Epoch
    {
        set {  _Epoch= value; } 
        get { return _Epoch; } 
    }
}

Here's how you would use such a thing during serialization:

        var o2= new MyTypeWithNamespaces { ..intializers.. };
        var builder = new System.Text.StringBuilder();
        using ( XmlWriter writer = new NoNamespaceXmlWriter(new System.IO.StringWriter(builder)))
        {
            s2.Serialize(writer, o2, ns2);
        }            
        Console.WriteLine("{0}",builder.ToString());

The XmlTextWriter is sort of broken, though. According to the reference doc, when it writes it does not check for the following:

• Invalid characters in attribute and element names.

• Unicode characters that do not fit the specified encoding. If the Unicode characters do not fit the specified encoding, the XmlTextWriter does not escape the Unicode characters into character entities.

• Duplicate attributes.

• Characters in the DOCTYPE public identifier or system identifier.

These problems with XmlTextWriter have been around since v1.1 of the .NET Framework, and they will remain, for backward compatibility. If you have no concerns about those problems, then by all means use the XmlTextWriter. But most people would like a bit more reliability.

To get that, while still suppressing namespaces during serialization, instead of deriving from XmlTextWriter, define a concrete implementation of the abstract XmlWriter and its 24 methods.

An example is here:

public class XmlWriterWrapper : XmlWriter
{
    protected XmlWriter writer;

    public XmlWriterWrapper(XmlWriter baseWriter)
    {
        this.Writer = baseWriter;
    }

    public override void Close()
    {
        this.writer.Close();
    }

    protected override void Dispose(bool disposing)
    {
        ((IDisposable) this.writer).Dispose();
    }

    public override void Flush()
    {
        this.writer.Flush();
    }

    public override string LookupPrefix(string ns)
    {
        return this.writer.LookupPrefix(ns);
    }

    public override void WriteBase64(byte[] buffer, int index, int count)
    {
        this.writer.WriteBase64(buffer, index, count);
    }

    public override void WriteCData(string text)
    {
        this.writer.WriteCData(text);
    }

    public override void WriteCharEntity(char ch)
    {
        this.writer.WriteCharEntity(ch);
    }

    public override void WriteChars(char[] buffer, int index, int count)
    {
        this.writer.WriteChars(buffer, index, count);
    }

    public override void WriteComment(string text)
    {
        this.writer.WriteComment(text);
    }

    public override void WriteDocType(string name, string pubid, string sysid, string subset)
    {
        this.writer.WriteDocType(name, pubid, sysid, subset);
    }

    public override void WriteEndAttribute()
    {
        this.writer.WriteEndAttribute();
    }

    public override void WriteEndDocument()
    {
        this.writer.WriteEndDocument();
    }

    public override void WriteEndElement()
    {
        this.writer.WriteEndElement();
    }

    public override void WriteEntityRef(string name)
    {
        this.writer.WriteEntityRef(name);
    }

    public override void WriteFullEndElement()
    {
        this.writer.WriteFullEndElement();
    }

    public override void WriteProcessingInstruction(string name, string text)
    {
        this.writer.WriteProcessingInstruction(name, text);
    }

    public override void WriteRaw(string data)
    {
        this.writer.WriteRaw(data);
    }

    public override void WriteRaw(char[] buffer, int index, int count)
    {
        this.writer.WriteRaw(buffer, index, count);
    }

    public override void WriteStartAttribute(string prefix, string localName, string ns)
    {
        this.writer.WriteStartAttribute(prefix, localName, ns);
    }

    public override void WriteStartDocument()
    {
        this.writer.WriteStartDocument();
    }

    public override void WriteStartDocument(bool standalone)
    {
        this.writer.WriteStartDocument(standalone);
    }

    public override void WriteStartElement(string prefix, string localName, string ns)
    {
        this.writer.WriteStartElement(prefix, localName, ns);
    }

    public override void WriteString(string text)
    {
        this.writer.WriteString(text);
    }

    public override void WriteSurrogateCharEntity(char lowChar, char highChar)
    {
        this.writer.WriteSurrogateCharEntity(lowChar, highChar);
    }

    public override void WriteValue(bool value)
    {
        this.writer.WriteValue(value);
    }

    public override void WriteValue(DateTime value)
    {
        this.writer.WriteValue(value);
    }

    public override void WriteValue(decimal value)
    {
        this.writer.WriteValue(value);
    }

    public override void WriteValue(double value)
    {
        this.writer.WriteValue(value);
    }

    public override void WriteValue(int value)
    {
        this.writer.WriteValue(value);
    }

    public override void WriteValue(long value)
    {
        this.writer.WriteValue(value);
    }

    public override void WriteValue(object value)
    {
        this.writer.WriteValue(value);
    }

    public override void WriteValue(float value)
    {
        this.writer.WriteValue(value);
    }

    public override void WriteValue(string value)
    {
        this.writer.WriteValue(value);
    }

    public override void WriteWhitespace(string ws)
    {
        this.writer.WriteWhitespace(ws);
    }


    public override XmlWriterSettings Settings
    {
        get
        {
            return this.writer.Settings;
        }
    }

    protected XmlWriter Writer
    {
        get
        {
            return this.writer;
        }
        set
        {
            this.writer = value;
        }
    }

    public override System.Xml.WriteState WriteState
    {
        get
        {
            return this.writer.WriteState;
        }
    }

    public override string XmlLang
    {
        get
        {
            return this.writer.XmlLang;
        }
    }

    public override System.Xml.XmlSpace XmlSpace
    {
        get
        {
            return this.writer.XmlSpace;
        }
    }        
}

Then, provide a derived class that overrides the StartElement method, as before:

public class NamespaceSupressingXmlWriter : XmlWriterWrapper
{
    //Provide as many contructors as you need
    public NamespaceSupressingXmlWriter(System.IO.TextWriter output)
        : base(XmlWriter.Create(output)) { }

    public NamespaceSupressingXmlWriter(XmlWriter output)
        : base(XmlWriter.Create(output)) { }

    public override void WriteStartElement(string prefix, string localName, string ns)
    {
        base.WriteStartElement("", localName, "");
    }
}

And then use this writer like so:

        var o2= new MyTypeWithNamespaces { ..intializers.. };
        var builder = new System.Text.StringBuilder();
        var settings = new XmlWriterSettings { OmitXmlDeclaration = true, Indent= true };
        using ( XmlWriter innerWriter = XmlWriter.Create(builder, settings))
            using ( XmlWriter writer = new NamespaceSupressingXmlWriter(innerWriter))
            {
                s2.Serialize(writer, o2, ns2);
            }            
        Console.WriteLine("{0}",builder.ToString());

Credit for this to Oleg Tkachenko.

After reading Microsoft's documentation and several solutions online, I have discovered the solution to this problem. It works with both the built-in XmlSerializer and custom XML serialization via IXmlSerialiazble.

To wit, I'll use the same MyTypeWithNamespaces XML sample that's been used in the answers to this question so far.

[XmlRoot("MyTypeWithNamespaces", Namespace="urn:Abracadabra", IsNullable=false)]
public class MyTypeWithNamespaces
{
    // As noted below, per Microsoft's documentation, if the class exposes a public
    // member of type XmlSerializerNamespaces decorated with the 
    // XmlNamespacesDeclarationAttribute, then the XmlSerializer will utilize those
    // namespaces during serialization.
    public MyTypeWithNamespaces( )
    {
        this._namespaces = new XmlSerializerNamespaces(new XmlQualifiedName[] {
            // Don't do this!! Microsoft's documentation explicitly says it's not supported.
            // It doesn't throw any exceptions, but in my testing, it didn't always work.

            // new XmlQualifiedName(string.Empty, string.Empty),  // And don't do this:
            // new XmlQualifiedName("", "")

            // DO THIS:
            new XmlQualifiedName(string.Empty, "urn:Abracadabra") // Default Namespace
            // Add any other namespaces, with prefixes, here.
        });
    }

    // If you have other constructors, make sure to call the default constructor.
    public MyTypeWithNamespaces(string label, int epoch) : this( )
    {
        this._label = label;
        this._epoch = epoch;
    }

    // An element with a declared namespace different than the namespace
    // of the enclosing type.
    [XmlElement(Namespace="urn:Whoohoo")]
    public string Label
    {
        get { return this._label; }
        set { this._label = value; }
    }
    private string _label;

    // An element whose tag will be the same name as the property name.
    // Also, this element will inherit the namespace of the enclosing type.
    public int Epoch
    {
        get { return this._epoch; }
        set { this._epoch = value; }
    }
    private int _epoch;

    // Per Microsoft's documentation, you can add some public member that
    // returns a XmlSerializerNamespaces object. They use a public field,
    // but that's sloppy. So I'll use a private backed-field with a public
    // getter property. Also, per the documentation, for this to work with
    // the XmlSerializer, decorate it with the XmlNamespaceDeclarations
    // attribute.
    [XmlNamespaceDeclarations]
    public XmlSerializerNamespaces Namespaces
    {
        get { return this._namespaces; }
    }
    private XmlSerializerNamespaces _namespaces;
}

That's all to this class. Now, some objected to having an XmlSerializerNamespaces object somewhere within their classes; but as you can see, I neatly tucked it away in the default constructor and exposed a public property to return the namespaces.

Now, when it comes time to serialize the class, you would use the following code:

MyTypeWithNamespaces myType = new MyTypeWithNamespaces("myLabel", 42);

/******
   OK, I just figured I could do this to make the code shorter, so I commented out the
   below and replaced it with what follows:

// You have to use this constructor in order for the root element to have the right namespaces.
// If you need to do custom serialization of inner objects, you can use a shortened constructor.
XmlSerializer xs = new XmlSerializer(typeof(MyTypeWithNamespaces), new XmlAttributeOverrides(),
    new Type[]{}, new XmlRootAttribute("MyTypeWithNamespaces"), "urn:Abracadabra");

******/
XmlSerializer xs = new XmlSerializer(typeof(MyTypeWithNamespaces),
    new XmlRootAttribute("MyTypeWithNamespaces") { Namespace="urn:Abracadabra" });

// I'll use a MemoryStream as my backing store.
MemoryStream ms = new MemoryStream();

// This is extra! If you want to change the settings for the XmlSerializer, you have to create
// a separate XmlWriterSettings object and use the XmlTextWriter.Create(...) factory method.
// So, in this case, I want to omit the XML declaration.
XmlWriterSettings xws = new XmlWriterSettings();
xws.OmitXmlDeclaration = true;
xws.Encoding = Encoding.UTF8; // This is probably the default
// You could use the XmlWriterSetting to set indenting and new line options, but the
// XmlTextWriter class has a much easier method to accomplish that.

// The factory method returns a XmlWriter, not a XmlTextWriter, so cast it.
XmlTextWriter xtw = (XmlTextWriter)XmlTextWriter.Create(ms, xws);
// Then we can set our indenting options (this is, of course, optional).
xtw.Formatting = Formatting.Indented;

// Now serialize our object.
xs.Serialize(xtw, myType, myType.Namespaces);

Once you have done this, you should get the following output:

<MyTypeWithNamespaces>
    <Label xmlns="urn:Whoohoo">myLabel</Label>
    <Epoch>42</Epoch>
</MyTypeWithNamespaces>

I have successfully used this method in a recent project with a deep hierachy of classes that are serialized to XML for web service calls. Microsoft's documentation is not very clear about what to do with the publicly accesible XmlSerializerNamespaces member once you've created it, and so many think it's useless. But by following their documentation and using it in the manner shown above, you can customize how the XmlSerializer generates XML for your classes without resorting to unsupported behavior or "rolling your own" serialization by implementing IXmlSerializable.

It is my hope that this answer will put to rest, once and for all, how to get rid of the standard xsi and xsd namespaces generated by the XmlSerializer.

UPDATE: I just want to make sure I answered the OP's question about removing all namespaces. My code above will work for this; let me show you how. Now, in the example above, you really can't get rid of all namespaces (because there are two namespaces in use). Somewhere in your XML document, you're going to need to have something like xmlns="urn:Abracadabra" xmlns:w="urn:Whoohoo. If the class in the example is part of a larger document, then somewhere above a namespace must be declared for either one of (or both) Abracadbra and Whoohoo. If not, then the element in one or both of the namespaces must be decorated with a prefix of some sort (you can't have two default namespaces, right?). So, for this example, Abracadabra is the defalt namespace. I could inside my MyTypeWithNamespaces class add a namespace prefix for the Whoohoo namespace like so:

public MyTypeWithNamespaces
{
    this._namespaces = new XmlSerializerNamespaces(new XmlQualifiedName[] {
        new XmlQualifiedName(string.Empty, "urn:Abracadabra"), // Default Namespace
        new XmlQualifiedName("w", "urn:Whoohoo")
    });
}

Now, in my class definition, I indicated that the <Label/> element is in the namespace "urn:Whoohoo", so I don't need to do anything further. When I now serialize the class using my above serialization code unchanged, this is the output:

<MyTypeWithNamespaces xmlns:w="urn:Whoohoo">
    <w:Label>myLabel</w:Label>
    <Epoch>42</Epoch>
</MyTypeWithNamespaces>

Because <Label> is in a different namespace from the rest of the document, it must, in someway, be "decorated" with a namespace. Notice that there are still no xsi and xsd namespaces.

XmlSerializer sr = new XmlSerializer(objectToSerialize.GetType());
TextWriter xmlWriter = new StreamWriter(filename);
XmlSerializerNamespaces namespaces = new XmlSerializerNamespaces();
namespaces.Add(string.Empty, string.Empty);
sr.Serialize(xmlWriter, objectToSerialize, namespaces);

This is the first of my two answers to the question.

If you want fine control over the namespaces - for example if you want to omit some of them but not others, or if you want to replace one namespace with another, you can do this using XmlAttributeOverrides.

Suppose you have this type definition:

// explicitly specify a namespace for this type,
// to be used during XML serialization.
[XmlRoot(Namespace="urn:Abracadabra")]
public class MyTypeWithNamespaces
{
    // private fields backing the properties
    private int _Epoch;
    private string _Label;

    // explicitly define a distinct namespace for this element
    [XmlElement(Namespace="urn:Whoohoo")]
    public string Label
    {
        set {  _Label= value; } 
        get { return _Label; } 
    }

    // this property will be implicitly serialized to XML using the
    // member name for the element name, and inheriting the namespace from
    // the type.
    public int Epoch
    {
        set {  _Epoch= value; } 
        get { return _Epoch; } 
    }
}

And this serialization pseudo-code:

        var o2= new MyTypeWithNamespaces() { ..initializers...};
        ns.Add( "", "urn:Abracadabra" );
        XmlSerializer s2 = new XmlSerializer(typeof(MyTypeWithNamespaces));
        s2.Serialize(System.Console.Out, o2, ns);

You would get something like this XML:

<MyTypeWithNamespaces xmlns="urn:Abracadabra">
  <Label xmlns="urn:Whoohoo">Cimsswybclaeqjh</Label>
  <Epoch>97</Epoch>
</MyTypeWithNamespaces>

Notice that there is a default namespace on the root element, and there is also a distinct namespace on the "Label" element. These namespaces were dictated by the attributes decorating the type, in the code above.

The Xml Serialization framework in .NET includes the possibility to explicitly override the attributes that decorate the actual code. You do this with the XmlAttributesOverrides class and friends. Suppose I have the same type, and I serialize it this way:

        // instantiate the container for all attribute overrides
        XmlAttributeOverrides xOver = new XmlAttributeOverrides();

        // define a set of XML attributes to apply to the root element
        XmlAttributes xAttrs1 = new XmlAttributes();

        // define an XmlRoot element (as if [XmlRoot] had decorated the type)
        // The namespace in the attribute override is the empty string. 
        XmlRootAttribute xRoot = new XmlRootAttribute() { Namespace = ""};

        // add that XmlRoot element to the container of attributes
        xAttrs1.XmlRoot= xRoot;

        // add that bunch of attributes to the container holding all overrides
        xOver.Add(typeof(MyTypeWithNamespaces), xAttrs1);

        // create another set of XML Attributes
        XmlAttributes xAttrs2 = new XmlAttributes();

        // define an XmlElement attribute, for a type of "String", with no namespace
        var xElt = new XmlElementAttribute(typeof(String)) { Namespace = ""};

        // add that XmlElement attribute to the 2nd bunch of attributes
        xAttrs2.XmlElements.Add(xElt);

        // add that bunch of attributes to the container for the type, and
        // specifically apply that bunch to the "Label" property on the type.
        xOver.Add(typeof(MyTypeWithNamespaces), "Label", xAttrs2);

        // instantiate a serializer with the overrides 
        XmlSerializer s3 = new XmlSerializer(typeof(MyTypeWithNamespaces), xOver);

        // serialize
        s3.Serialize(System.Console.Out, o2, ns2);

The result looks like this;

<MyTypeWithNamespaces>
  <Label>Cimsswybclaeqjh</Label>
  <Epoch>97</Epoch>
</MyTypeWithNamespaces>

You have stripped the namespaces.

A logical question is, can you strip all namespaces from arbitrary types during serialization, without going through the explicit overrides? The answer is YES, and how to do it is in my next response.